[선재] WEEK09 Solution

find-minimum-in-rotated-sorted-array/sunjae95.js

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+/**
+ * @description
+ * brainstorming:
+ * brute force
+ *
+ * n = length of head
+ * time complexity: O(n)
+ * space complexity: O(1)
+ */
+var findMin = function (nums) {
+  let answer = 5000;
+  nums.forEach((num) => (answer = Math.min(answer, num)));
+
+  return answer;
+};
+
+/* n = length of head
+ * time complexity: O(n)
+ * space complexity: O(1)
+ */
+var findMin = function (nums) {
+  let answer = nums[0];
+  if (nums.length === 1) return answer;
+  if (answer < nums[nums.length - 1]) return answer;
+
+  for (let i = nums.length - 1; i >= 0; i--) {
+    if (answer < nums[i]) return answer;
+    answer = nums[i];
+  }
+
+  return answer;
+};

linked-list-cycle/sunjae95.js

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+/**
+ * @description
+ * brainstorming:
+ * hash table
+ *
+ * n = length of head
+ * time complexity: O(n)
+ * space complexity: O(n)
+ */
+var hasCycle = function (head) {
+  const set = new Set();
+  let node = head;
+
+  while (node) {
+    if (set.has(node)) return true;
+    set.add(node);
+    node = node.next;
+  }
+
+  return false;
+};

maximum-subarray/sunjae95.js

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+/**
+ * @description
+ * n = length of nums
+ * time complexity: O(n)
+ * space complexity: O(1)
+ */
+var maxSubArray = function (nums) {
+  let sum = 0;
+  let answer = nums[0];
+
+  for (let end = 0; end < nums.length; end++) {
+    if (sum < 0) {
+      sum = nums[end];
+    } else if (sum + nums[end] >= 0) {
+      sum += nums[end];
+    } else {
+      sum = nums[end];
+    }
+
+    answer = Math.max(answer, sum);
+  }
+  return answer;
+};

minimum-window-substring/sunjae.js

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+/**
+ * @description
+ * brainstorming:
+ * two pointer + hash table
+ *
+ * n = length of s
+ * m = length of t
+ * time complexity: O(n*n)
+ * space complexity: O(n)
+ */
+var minWindow = function (s, t) {
+  const requiredMap = t.split("").reduce((map, char) => {
+    map.set(char, (map.get(char) ?? 0) + 1);
+    return map;
+  }, new Map());
+  const requiredArray = [...requiredMap.entries()];
+  const map = new Map();
+  const successRequired = () =>
+    requiredArray.every(([key, value]) => map.get(key) >= value);
+
+  let answer = "";
+  let start = 0;
+
+  for (let i = 0; i < s.length; i++) {
+    if (requiredMap.has(s[i])) map.set(s[i], (map.get(s[i]) ?? 0) + 1);
+
+    while (successRequired()) {
+      const now = s.slice(start, i + 1);
+      answer = answer === "" || answer.length >= now.length ? now : answer;
+
+      if (map.has(s[start])) {
+        map.set(s[start], map.get(s[start]) - 1);
+        if (map.get(s[start]) === -1) map.delete(s[start]);
+      }
+
+      start++;
+    }
+  }
+
+  return answer;
+};

pacific-atlantic-water-flow/sunjae95.js

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+/**
+ * @description
+ * brainstorming:
+ * bfs + memoization
+ *
+ * n = length of height
+ * m = length of height[i]
+ * time complexity: O(n*m * 4^n*m)
+ * space complexity: O(n*m)
+ */
+var pacificAtlantic = function (heights) {
+  const visited = Array.from({ length: heights.length }, (_, i) =>
+    Array.from({ length: heights[i].length }, () => false)
+  );
+  const memo = new Map();
+
+  const bfs = (row, column) => {
+    const dr = [0, 0, -1, 1];
+    const dc = [1, -1, 0, 0];
+    const queue = [[row, column]];
+    let [pacific, atlantic] = [false, false];
+    let queueIndex = 0;
+
+    while (queueIndex !== queue.length) {
+      const currentLastLength = queue.length;
+
+      while (queueIndex !== currentLastLength) {
+        const [r, c] = queue[queueIndex++];
+        visited[r][c] = `${row},${column}`;
+
+        if (memo.has(`${r},${c}`)) {
+          memo.set(`${row},${column}`, [row, column]);
+          return;
+        }
+
+        for (let i = 0; i < 4; i++) {
+          const nextR = r + dr[i];
+          const nextC = c + dc[i];
+          const isPacific = nextR === -1 || nextC === -1;
+          const isAtlantic =
+            nextR === heights.length || nextC === heights[0].length;
+
+          if (isPacific) {
+            pacific = true;
+            continue;
+          }
+          if (isAtlantic) {
+            atlantic = true;
+            continue;
+          }
+
+          if (visited[nextR][nextC] === `${row},${column}`) continue;
+
+          if (heights[r][c] < heights[nextR][nextC]) continue;
+
+          queue.push([nextR, nextC]);
+        }
+      }
+
+      if (pacific && atlantic) {
+        memo.set(`${row},${column}`, [row, column]);
+        return;
+      }
+    }
+  };
+
+  for (let row = 0; row < heights.length; row++) {
+    for (let column = 0; column < heights[row].length; column++) {
+      bfs(row, column);
+    }
+  }
+
+  return [...memo.values()];
+};