[krokerdile] Week 11 Solutions

longest-repeating-character-replacement/krokerdile.js

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+/**
+ * @param {string} s
+ * @param {number} k
+ * @return {number}
+ */
+var characterReplacement = function(s, k) {
+    let left = 0;
+    let maxCount = 0;
+    const freq = new Array(26).fill(0); // 알파벳 빈도수 저장
+
+    let result = 0;
+
+    for (let right = 0; right < s.length; right++) {
+        const idx = s.charCodeAt(right) - 65; // A ~ Z -> 0 ~ 25
+        freq[idx]++;
+        maxCount = Math.max(maxCount, freq[idx]);
+
+        // 현재 윈도우 크기 - 가장 많은 문자 수 > k 면 왼쪽 포인터 이동
+        while ((right - left + 1) - maxCount > k) {
+            freq[s.charCodeAt(left) - 65]--;
+            left++;
+        }
+
+        result = Math.max(result, right - left + 1);
+    }
+
+    return result;
+};

minimum-window-substring/krokerdile.js

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+/**
+ * @param {string} s
+ * @param {string} t
+ * @return {string}
+ */
+var minWindow = function(s, t) {
+    if (s.length < t.length) return "";
+
+    // 1. t의 문자 개수를 세기
+    const targetMap = new Map();
+    for (let char of t) {
+        targetMap.set(char, (targetMap.get(char) || 0) + 1);
+    }
+
+    let left = 0;
+    let right = 0;
+    let minLen = Infinity;
+    let minStart = 0;
+
+    let required = targetMap.size; // 만족시켜야 할 문자 종류 수
+    let formed = 0;
+    const windowMap = new Map();
+
+    while (right < s.length) {
+        const char = s[right];
+        windowMap.set(char, (windowMap.get(char) || 0) + 1);
+
+        // 문자 개수가 딱 맞는 경우
+        if (targetMap.has(char) && windowMap.get(char) === targetMap.get(char)) {
+            formed++;
+        }
+
+        // 모든 문자가 충족될 경우 -> 왼쪽 포인터 당겨보기
+        while (left <= right && formed === required) {
+            if (right - left + 1 < minLen) {
+                minLen = right - left + 1;
+                minStart = left;
+            }
+
+            const leftChar = s[left];
+            windowMap.set(leftChar, windowMap.get(leftChar) - 1);
+            if (targetMap.has(leftChar) && windowMap.get(leftChar) < targetMap.get(leftChar)) {
+                formed--;
+            }
+            left++;
+        }
+
+        right++;
+    }
+
+    return minLen === Infinity ? "" : s.slice(minStart, minStart + minLen);
+};

pacific-atlantic-water-flow/krokerdile.js

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+/**
+ * @param {number[][]} heights
+ * @return {number[][]}
+ */
+const pacificAtlantic = (heights) => {
+  const m = heights.length;
+  const n = heights[0].length;
+  const pacific = Array.from({ length: m }, () => Array(n).fill(false));
+  const atlantic = Array.from({ length: m }, () => Array(n).fill(false));
+
+  const dfs = (r, c, visited, prevHeight) => {
+    if (
+      r < 0 || c < 0 || r >= m || c >= n || 
+      visited[r][c] || heights[r][c] < prevHeight
+    ) return;
+
+    visited[r][c] = true;
+
+    dfs(r + 1, c, visited, heights[r][c]);
+    dfs(r - 1, c, visited, heights[r][c]);
+    dfs(r, c + 1, visited, heights[r][c]);
+    dfs(r, c - 1, visited, heights[r][c]);
+  };
+
+  for (let i = 0; i < m; i++) {
+    dfs(i, 0, pacific, heights[i][0]);
+    dfs(i, n - 1, atlantic, heights[i][n - 1]);
+  }
+
+  for (let j = 0; j < n; j++) {
+    dfs(0, j, pacific, heights[0][j]);
+    dfs(m - 1, j, atlantic, heights[m - 1][j]);
+  }
+
+  const result = [];
+  for (let i = 0; i < m; i++) {
+    for (let j = 0; j < n; j++) {
+      if (pacific[i][j] && atlantic[i][j]) {
+        result.push([i, j]);
+      }
+    }
+  }
+  return result;
+};