[sora0319] WEEK 01 solutions

contains-duplicate/sora0319.java

@@ -1,4 +1,21 @@
 import java.util.*;
+// 개선 방향
+class Solution {
+    public boolean containsDuplicate(int[] nums) {
+        Set duplication = new HashSet<>();
+
+        for(int n : nums){
+            if(duplication.contains(n)){
+               return true;
+            }
+            duplication.add(n);
+        }
+        return false;
+    }
+}
+
+
+// 초기 문제 풀이
 class Solution {
     public boolean containsDuplicate(int[] nums) {
         Arrays.sort(nums);

house-robber/sora0319.java

@@ -1,4 +1,20 @@
 import java.util.*;
+// 2번째 풀이
+class Solution {
+    public int rob(int[] nums) {
+        int[] dp = new int[nums.length+1];
+        dp[1] = nums[0];
+
+        for(int i = 1; i < nums.length; i++){
+            dp[i+1] = Math.max(dp[i-1] + nums[i], dp[i]);
+        }
+        return dp[nums.length];
+    }
+}
+
+
+
+// 1번째 풀이
 class Solution {
     public int rob(int[] nums) {
         int[] house = new int[nums.length];

longest-consecutive-sequence/sora0319.java

@@ -1,5 +1,28 @@
 import java.util.*;
+// 2번째 푼 코드
+class Solution {
+    public int longestConsecutive(int[] nums) {
+       Set<Integer> set = new HashSet<>();
+        for (int n : nums) {
+            set.add(n);
+        }
+
+        int cntMax = 0;
+        for (int n : set) {  
+            if (!set.contains(n - 1)) {
+                int end = n;
+                while (set.contains(end + 1)) {
+                    end++;
+                }
+                cntMax = Math.max(cntMax, end - n + 1);
+            }
+        }
+
+        return cntMax;
+    }
+}
 
+// 처음 풀어본 코드
 class Solution {
     public int longestConsecutive(int[] nums) {
         Set<Integer> checkList = new HashSet<>();

top-k-frequent-elements/sora0319.java

@@ -1,5 +1,29 @@
 import java.util.*;
+// 다른 방안
+class Solution {
+    public int[] topKFrequent(int[] nums, int k) {
+        Map <Integer,Integer> counting = new HashMap<>();
+
+        for(int n : nums){
+            if(!counting.containsKey(n)){
+                counting.put(n,0);
+            }
+            counting.put(n, counting.get(n)+1);
+        }
+
+        List<Map.Entry<Integer,Integer>>countList = new LinkedList<>(counting.entrySet());
+        countList.sort(Map.Entry.comparingByValue(Comparator.reverseOrder()));
+
+        int[] answer = countList.stream()
+        .limit(k)
+        .mapToInt(Map.Entry::getKey)
+        .toArray();
+        return answer;
+    }
+}
+
 
+// 초안
 class Solution {
     public int[] topKFrequent(int[] nums, int k) {
         Map<Integer,Integer> counts = new HashMap<>();

two-sum/sora0319.java

@@ -1,4 +1,23 @@
 import java.util.*;
+
+// 개선안
+class Solution {
+    public int[] twoSum(int[] nums, int target) {
+        Map<Integer,Integer> checkNums = new HashMap<>();
+
+        for(int i = 0; i < nums.length; i++){
+            if(checkNums.containsKey(target - nums[i])){
+                int place = checkNums.get(target - nums[i]);
+                return new int[]{place, i};
+            }
+            checkNums.put(nums[i], i);
+        }
+        return new int[]{};
+    }
+}
+
+
+// 초기 구성안
 class Solution {
     public int[] twoSum(int[] nums, int target) {
         Map<Integer,Integer> element = new HashMap<>();