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Merge pull request DaleStudy#1524 from Tessa1217/main
[Tessa1217] Week 09 Solutions
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β€Žlinked-list-cycle/Tessa1217.java

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/**
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* Definition for singly-linked list.
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* class ListNode {
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* int val;
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* ListNode next;
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* ListNode(int x) {
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* val = x;
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* next = null;
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* }
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* }
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*/
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/**
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* headλŠ” μ—°κ²° 리슀트의 ν—€λ“œλ‹€.
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* νŠΉμ • λ…Έλ“œκ°€ 리슀트 λ‚΄μ˜ λ‹€λ₯Έ λ…Έλ“œμ™€ next 포인트λ₯Ό 톡해 μ—°κ²°λ˜μ–΄ μžˆμ„ λ•Œ 이 λ¦¬μŠ€νŠΈμ—λŠ” 사이클이 μžˆλ‹€κ³  ν•  수 μžˆλ‹€.
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* posλŠ” next 포인터와 μ—°κ²°λœ λ…Έλ“œμ˜ 인덱슀λ₯Ό λ‚˜νƒ€λ‚΄λŠ”λ° 쓰이며 posλŠ” νŒŒλΌλ―Έν„°λ‘œ 주어지지 μ•ŠλŠ”λ‹€.
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* 주어진 λ¦¬μŠ€νŠΈμ— 사이클이 μžˆλ‹€λ©΄ trueλ₯Ό 그렇지 μ•Šλ‹€λ©΄ falseλ₯Ό λ°˜ν™˜ν•˜μ„Έμš”.
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* */
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public class Solution {
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// μ‹œκ°„λ³΅μž‘λ„: O(n), κ³΅κ°„λ³΅μž‘λ„: O(1)
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public boolean hasCycle(ListNode head) {
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if (head == null) {
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return false;
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}
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ListNode next = head;
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ListNode furtherNext = head;
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while (furtherNext != null && furtherNext.next != null) {
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next = next.next;
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furtherNext = furtherNext.next.next;
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if (next == furtherNext) {
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return true;
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}
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}
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return false;
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}
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// head 없을 λ•ŒκΉŒμ§€ 계속 탐색 반볡 : μ‹œκ°„λ³΅μž‘λ„, κ³΅κ°„λ³΅μž‘λ„ O(n)
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// public boolean hasCycle(ListNode head) {
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// Set<ListNode> nodeSet = new HashSet<>();
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// while (head != null) {
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// if (nodeSet.contains(head)) {
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// return true;
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// }
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// nodeSet.add(head);
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// head = head.next;
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// }
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// return false;
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// }
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}
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β€Žmaximum-product-subarray/Tessa1217.java

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class Solution {
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// μ‹œκ°„λ³΅μž‘λ„: O(n)
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public int maxProduct(int[] nums) {
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if (nums == null || nums.length == 0) {
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return 0;
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}
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// μ΅œλŒ€ κ³± μΌ€μ΄μŠ€
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int maxProduct = nums[0];
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// μ΅œμ†Œ κ³± μΌ€μ΄μŠ€
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int minProduct = nums[0];
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// μ΅œλŒ€ κ°’
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int max = nums[0];
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// DP둜 ν’€μ΄ν•˜μ˜€μ§€λ§Œ 음수 * 음수의 λ°˜λ‘€ μΌ€μ΄μŠ€ λ°œμƒν•˜μ—¬ ν•΄λ‹Ή ν’€μ΄λ‘œ μˆ˜μ •
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// Test Case : [-2, 3, -4] => dp둜 풀이 μ‹œ 3이 λ°˜ν™˜λ˜λŠ” 문제 μžˆμ—ˆμŒ
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for (int i = 1; i < nums.length; i++) {
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int current = nums[i];
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// 음수일 경우 : μ΅œμ†Œ κ³±κ³Ό μ΅œλŒ€ κ³± μœ„μΉ˜ λ°”κΏˆ
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if (current < 0) {
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int tempMax = maxProduct;
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maxProduct = Math.max(current, minProduct * current);
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minProduct = Math.min(current, tempMax * current);
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} else {
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maxProduct = Math.max(current, maxProduct * current);
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minProduct = Math.min(current, minProduct * current);
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}
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max = Math.max(max, maxProduct);
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}
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return max;
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}
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}
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β€Žminimum-window-substring/Tessa1217.java

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import java.util.HashMap;
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import java.util.Map;
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class Solution {
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// μ‹œκ°„λ³΅μž‘λ„: O(n), κ³΅κ°„λ³΅μž‘λ„ O(1)
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public String minWindow(String s, String t) {
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int strLength = s.length();
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int targetLength = t.length();
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// λͺ©ν‘œ λΆ„μžμ—΄μ΄ 주어진 λ¬Έμžμ—΄λ³΄λ‹€ κΈΈλ‹€λ©΄ λΆ€λΆ„ λ¬Έμžμ—΄λ‘œ λ³Ό 수 μ—†μŒ
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if (targetLength > strLength) {
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return "";
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}
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// λͺ©ν‘œ λ¬Έμžμ—΄μ— ν•„μš”ν•œ λ¬Έμžμ™€ κ·Έ 개수λ₯Ό λ‹΄λŠ” 맡
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Map<Character, Integer> charMap = new HashMap<>();
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for (char c : t.toCharArray()) {
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charMap.put(c, charMap.getOrDefault(c, 0) + 1);
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}
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// 투 포인터 μ„ μ–Έ
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int left = 0;
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int right = 0;
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int minWindowLength = Integer.MAX_VALUE;
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int minWindowStart = 0; // μ΅œμ†Œ μœˆλ„μš° μ‹œμž‘ μœ„μΉ˜
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int remaining = targetLength;
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while (right < strLength) {
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Character end = s.charAt(right);
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if (charMap.containsKey(end)) {
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charMap.put(end, charMap.get(end) - 1);
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if (charMap.get(end) >= 0) {
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remaining--;
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}
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}
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// target λ¬Έμžμ—΄μ˜ λͺ¨λ“  문자λ₯Ό μ°Ύμ•˜λ‹€λ©΄ left 포인터 μ΄λ™ν•˜λ©΄μ„œ
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// μ΅œμ†Œ μœˆλ„μš° μ°ΎκΈ° μ‹œμž‘
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while (remaining == 0) {
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if (right - left + 1 < minWindowLength) {
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minWindowLength = right - left + 1;
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minWindowStart = left;
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}
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char startChar = s.charAt(left);
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if (charMap.containsKey(startChar)) {
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charMap.put(startChar, charMap.get(startChar) + 1);
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if (charMap.get(startChar) > 0) {
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remaining++;
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}
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}
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left++;
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}
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right++;
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}
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return minWindowLength == Integer.MAX_VALUE ? ""
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: s.substring(minWindowStart, minWindowStart + minWindowLength);
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}
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}
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β€Žpacific-atlantic-water-flow/Tessa1217.java

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import java.util.ArrayList;
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import java.util.List;
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class Solution {
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int[] dx = {1, -1, 0, 0};
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int[] dy = {0, 0, 1, -1};
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// boolean[][] visited;
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int width, height;
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// μ‹œκ°„λ³΅μž‘λ„, κ³΅κ°„λ³΅μž‘λ„: O(m * n)
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public List<List<Integer>> pacificAtlantic(int[][] heights) {
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height = heights.length;
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width = heights[0].length;
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boolean[][] pacific = new boolean[height][width];
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boolean[][] atlantic = new boolean[height][width];
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/**
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* κ°€μž₯μžλ¦¬μ— λ„λ‹¬ν•˜λŠ” 경둜λ₯Ό 일일이 νƒμƒ‰ν•˜λŠ” 것이 μ•„λ‹Œ
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κ°€μž₯μžλ¦¬λΆ€ν„° 물이 흐λ₯Ό 수 μžˆλŠ” 경둜λ₯Ό μ—­μœΌλ‘œ 탐색
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*/
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// height check
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for (int i = 0; i < height; i++) {
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dfs(i, 0, heights, pacific);
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dfs(i, width - 1, heights, atlantic);
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}
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// width check
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for (int j = 0; j < width; j++) {
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dfs(0, j, heights, pacific);
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dfs(height - 1, j, heights, atlantic);
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}
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List<List<Integer>> answer = new ArrayList<>();
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for (int i = 0; i < height; i++) {
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for (int j = 0; j < width; j++) {
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if (pacific[i][j] && atlantic[i][j]) {
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answer.add(List.of(i, j));
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}
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}
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}
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return answer;
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}
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private void dfs(int x, int y, int[][] heights, boolean[][] visited) {
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visited[x][y] = true;
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for (int i = 0; i < 4; i++) {
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int nx = x + dx[i];
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int ny = y + dy[i];
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if (nx >= 0 && nx < height && ny >= 0 && ny < width) {
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if (!visited[nx][ny] && heights[nx][ny] >= heights[x][y]) {
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dfs(nx, ny, heights, visited);
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}
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}
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}
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}
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// public List<List<Integer>> pacificAtlantic(int[][] heights) {
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// height = heights.length;
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// width = heights[0].length;
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// visited = new boolean[height][width];
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// List<List<Integer>> answer = new ArrayList<>();
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// for (int i = 0; i < height; i++) {
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// for (int j = 0; j < width; j++) {
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// WaterFlow checkWaterFlow = dfs(i, j, new WaterFlow(), heights);
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// if (checkWaterFlow.crossBothOceans()) {
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// List<Integer> coordinate = List.of(i, j);
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// answer.add(coordinate);
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// }
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// }
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// }
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// return answer;
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// }
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// private WaterFlow dfs(int x, int y, WaterFlow checkWaterFlow, int[][] heights) {
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// /**
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// 0, 0 | 0, 1 | 0, 2 | 0, 3 | 0, 4
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// 1, 0 | 2, 0 | 3, 0 | 4, 0
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// */
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// if (x == 0 || y == 0) {
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// checkWaterFlow.crossPacificFlow();
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// }
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// /**
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// 4, 0 | 4, 1 | 4, 2 | 4, 3 | 4, 4
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// 3, 4 | 2, 4 | 1, 4 | 0, 4
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// */
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// if (x == height - 1 || y == width - 1) {
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// checkWaterFlow.crossAtlanticFlow();
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// }
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// if (checkWaterFlow.crossBothOceans()) {
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// return checkWaterFlow;
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// }
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// visited[x][y] = true;
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// for (int i = 0; i < 4; i++) {
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// int nx = x + dx[i];
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// int ny = y + dy[i];
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// if (nx >= 0 && nx < height && ny >= 0 && ny < width) {
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// if (!visited[nx][ny] && heights[nx][ny] <= heights[x][y]) {
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// dfs(nx, ny, checkWaterFlow, heights);
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// }
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// }
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// }
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// visited[x][y] = false;
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// return checkWaterFlow;
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// }
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// static class WaterFlow {
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// private boolean pacificFlow;
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// private boolean atlanticFlow;
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// WaterFlow() {
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// pacificFlow = false;
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// atlanticFlow = false;
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// }
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// public void crossPacificFlow() {
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// pacificFlow = true;
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// }
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// public void crossAtlanticFlow() {
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// atlanticFlow = true;
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// }
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// public boolean crossBothOceans() {
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// return pacificFlow && atlanticFlow;
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// }
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// }
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}
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β€Žsum-of-two-integers/Tessa1217.java

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/** +, - λΆ€ν˜Έ 쓰지 μ•Šκ³  두 수의 ν•© κ΅¬ν•˜κΈ° */
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class Solution {
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// λΉ„νŠΈ μ—°μ‚°μœΌλ‘œ 계산 μˆ˜ν–‰
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public int getSum(int a, int b) {
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while (b != 0) {
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// μ™Όμͺ½ μ‰¬ν”„νŠΈν•˜μ—¬ 자리 μ˜¬λ¦Όμ— λŒ€ν•œ 계산 μˆ˜ν–‰
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int bit = (a & b) << 1;
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// XOR μ—°μ‚°μœΌλ‘œ 자리 올림 μ—†λŠ” λ§μ…ˆ μˆ˜ν–‰
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a = a ^ b;
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b = bit;
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}
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return a;
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}
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/**
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* ν’€λ¦¬κΈ°λŠ” ν•˜μ§€λ§Œ, 이런 식은 νŽΈλ²•μΌ 것 같은...?
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* Class Integer 내뢀에 sum μ—°μ‚°: Adds two integers together as per the + operator.
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* + operator μ“΄λ‹€κ³  λ˜μ–΄μžˆμŒ...
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* */
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// public int getSum(int a, int b) {
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// return Integer.sum(a, b);
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// }
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}
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