[seueooo] WEEK 04 Solutions

coin-change/seueooo.js

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+/**
+ * bfs
+ * 시간 복잡도: O(amount * n)
+ * 공간 복잡도: O(amount)
+ * @param {number[]} coins
+ * @param {number} amount
+ * @return {number}
+ */
+var coinChange = function (coins, amount) {
+  let q = [];
+  let visited = new Set();
+  q.push([0, 0]);
+  while (q.length) {
+    const [sum, count] = q.shift();
+    if (sum === amount) return count;
+    if (visited.has(sum)) continue;
+    visited.add(sum);
+    for (let i = 0; i < coins.length; i++) {
+      const nextSum = sum + coins[i];
+      if (nextSum <= amount) {
+        q.push([nextSum, count + 1]);
+      }
+    }
+  }
+  return -1;
+};

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

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+/**
+이분 탐색
+시간 복잡도 : O(log n)
+공간 복잡도 : O(1)
+ * @param {number[]} nums
+ * @return {number}
+ */
+var findMin = function (nums) {
+  let left = 0;
+  let right = nums.length - 1;
+
+  while (left < right) {
+    let mid = Math.floor((left + right) / 2);
+    if (nums[mid] > nums[right]) {
+      left = mid + 1;
+    } else {
+      right = mid;
+    }
+  }
+
+  return nums[left];
+};

maximum-depth-of-binary-tree/seueooo.js

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+/**
+재귀
+ * Definition for a binary tree node.
+ * function TreeNode(val, left, right) {
+ *     this.val = (val===undefined ? 0 : val)
+ *     this.left = (left===undefined ? null : left)
+ *     this.right = (right===undefined ? null : right)
+ * }
+ */
+/**
+ * @param {TreeNode} root
+ * @return {number}
+ */
+var maxDepth = function (root) {
+  if (!root) return 0;
+  return 1 + Math.max(maxDepth(root.left), maxDepth(root.right));
+};

merge-two-sorted-lists/seueooo.js

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+/**
+ * 풀이
+ * 더 작은 노드를 머리로 두고, 그 next에 나머지를 병합한 결과를 연결.
+ * 최종적으로 머리를 반환
+ *
+ * 시간복잡도 - O(n + m) : n, m은 각각 list1, list2의 길이
+ * 공간복잡도 - O(n + m) : 재귀 호출 스택
+ *
+ * Definition for singly-linked list.
+ * function ListNode(val, next) {
+ *     this.val = (val===undefined ? 0 : val)
+ *     this.next = (next===undefined ? null : next)
+ * }
+ */
+/**
+ * @param {ListNode} list1
+ * @param {ListNode} list2
+ * @return {ListNode}
+ */
+var mergeTwoLists = function (list1, list2) {
+  if (!list1) return list2;
+  if (!list2) return list1;
+
+  if (list1.val <= list2.val) {
+    list1.next = mergeTwoLists(list1.next, list2);
+    return list1;
+  } else {
+    list2.next = mergeTwoLists(list1, list2.next);
+    return list2;
+  }
+};

word-search/seueooo.js

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+/**
+현재 경로를 하나 선택해서 끝까지 진행하고, 실패하면 방문 표시를 되돌려 다른 경로를 시도
+bfs, 백트래킹
+ * @param {character[][]} board
+ * @param {string} word
+ * @return {boolean}
+ */
+var exist = function (board, word) {
+  const rows = board.length;
+  const cols = board[0].length;
+
+  const dx = [-1, 1, 0, 0];
+  const dy = [0, 0, -1, 1];
+
+  function dfs(x, y, index) {
+    if (board[y][x] !== word[index]) {
+      return false;
+    }
+
+    if (index === word.length - 1) {
+      return true;
+    }
+
+    // 방문 처리
+    const original = board[y][x];
+    board[y][x] = "#";
+
+    for (let i = 0; i < 4; i++) {
+      const nx = x + dx[i];
+      const ny = y + dy[i];
+
+      if (
+        nx >= 0 &&
+        nx < cols &&
+        ny >= 0 &&
+        ny < rows &&
+        board[ny][nx] !== "#"
+      ) {
+        if (dfs(nx, ny, index + 1)) {
+          board[y][x] = original;
+          return true;
+        }
+      }
+    }
+
+    board[y][x] = original;
+    return false;
+  }
+
+  for (let i = 0; i < rows; i++) {
+    for (let j = 0; j < cols; j++) {
+      if (dfs(j, i, 0)) return true;
+    }
+  }
+  return false;
+};