[선재] WEEK06 문제 풀이

container-with-most-water/sunjae95.js

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+/**
+ * @description
+ * brainstorming:
+ * 1. brute force -> time limited
+ * 2. two pointer
+ *
+ * n: length of height
+ * time complexity: O(n)
+ * space complexity: O(1)
+ */
+var maxArea = function (height) {
+  let answer = 0;
+  let start = 0;
+  let end = height.length - 1;
+
+  while (start !== end) {
+    const w = end - start;
+    const h = Math.min(height[start], height[end]);
+    answer = Math.max(answer, w * h);
+    if (height[start] >= height[end]) {
+      end--;
+    } else if (height[start] < height[end]) {
+      start++;
+    }
+  }
+
+  return answer;
+};

longest-increasing-subsequence/sunjae95.js

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+/**
+ * @description
+ * brainstorming:
+ * 1. dfs -> time limited
+ * 2. memoization + dfs
+ *
+ * n: length of nums
+ * time complexity: O(n^2)
+ * space complexity: O(n)
+ */
+var lengthOfLIS = function (nums) {
+  const memo = new Array(nums.length).fill(-1);
+  let answer = 0;
+
+  const dfs = (index) => {
+    if (memo[index] !== -1) return memo[index];
+
+    let maxLength = 1;
+
+    for (let i = index + 1; i < nums.length; i++) {
+      if (nums[index] < nums[i]) {
+        maxLength = Math.max(maxLength, 1 + dfs(i));
+      }
+    }
+
+    memo[index] = maxLength;
+    return maxLength;
+  };
+
+  for (let i = 0; i < nums.length; i++) {
+    answer = Math.max(answer, dfs(i));
+  }
+
+  return answer;
+};

spiral-matrix/sunjae95.js

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+/**
+ * @description
+ * brainstorming:
+ * just implement question
+ *
+ * m: length of matrix
+ * n: length of matrix[i]
+ * time complexity: O(m * n)
+ * space complexity: O(m * n)
+ */
+var spiralOrder = function (matrix) {
+  let count = matrix.length * matrix[0].length;
+  let [r, c] = [1, 1];
+  const answer = [];
+  const MAX_R = matrix.length + 2;
+  const MAX_C = matrix[0].length + 2;
+  const visited = Array.from({ length: MAX_R }, (_, i) => {
+    return Array.from(
+      { length: MAX_C },
+      (_, j) => i === 0 || i === MAX_R - 1 || j === 0 || j === MAX_C - 1
+    );
+  });
+
+  while (count--) {
+    const check = {
+      left: c >= 1 && visited[r][c - 1],
+      right: c < MAX_C - 1 && visited[r][c + 1],
+      top: r >= 1 && visited[r - 1][c],
+      bottom: r < MAX_R - 1 && visited[r + 1][c],
+    };
+    visited[r][c] = true;
+    answer.push(matrix[r - 1][c - 1]);
+
+    if (check.left && check.top && check.bottom) c++;
+    else if (check.left && check.top && check.right) r++;
+    else if (check.right && check.top && check.bottom) c--;
+    else if (check.left && check.right && check.bottom) r--;
+    else if (check.left && check.top) c++;
+    else if (check.top && check.right) r++;
+    else if (check.right && check.bottom) c--;
+    else if (check.bottom && check.left) r--;
+  }
+
+  return answer;
+};

valid-parentheses/sunjae95.js

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+/**
+ * @description
+ * brainstorming:
+ * stack
+ *
+ * n: length of s
+ * time complexity: O(n)
+ * space complexity: O(n)
+ */
+var isValid = function (s) {
+  const stack = [];
+
+  for (let i = 0; i < s.length; i++) {
+    if (s[i] === "(" || s[i] === "{" || s[i] === "[") {
+      stack.push(s[i]);
+      continue;
+    }
+
+    const top = stack.length ? stack[stack.length - 1] : null;
+    if (top === null) return false;
+
+    if (
+      (top === "(" && s[i] === ")") ||
+      (top === "{" && s[i] === "}") ||
+      (top === "[" && s[i] === "]")
+    ) {
+      stack.pop();
+    } else return false;
+  }
+
+  return !stack.length;
+};