[ganu] Week4

coin-change/gwbaik9717.js

@@ -0,0 +1,23 @@
+// n: amount m: length of coins
+// Time complexity: O(n * m) + O(mlogm)
+// Space complexity: O(n)
+
+/**
+ * @param {number[]} coins
+ * @param {number} amount
+ * @return {number}
+ */
+var coinChange = function (coins, amount) {
+  const dp = Array.from({ length: amount + 1 }, () => Infinity);
+  dp[0] = 0;
+
+  coins.sort((a, b) => a - b);
+
+  for (const coin of coins) {
+    for (let i = coin; i <= amount; i++) {
+      dp[i] = Math.min(dp[i], dp[i - coin] + 1);
+    }
+  }
+
+  return dp.at(-1) === Infinity ? -1 : dp.at(-1);
+};

merge-two-sorted-lists/gwbaik9717.js

@@ -0,0 +1,42 @@
+// m: list1, n: list2
+// Time complexity: O(m+n)
+// Space complexity: O(m+n)
+
+/**
+ * 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) {
+  const answer = new ListNode();
+  let current = answer;
+
+  while (list1 && list2) {
+    if (list1.val < list2.val) {
+      current.next = list1;
+      list1 = list1.next;
+    } else {
+      current.next = list2;
+      list2 = list2.next;
+    }
+
+    current = current.next;
+  }
+
+  if (list1) {
+    current.next = list1;
+  }
+
+  if (list2) {
+    current.next = list2;
+  }
+
+  return answer.next;
+};

missing-number/gwbaik9717.js

@@ -0,0 +1,15 @@
+// Time complexity: O(n)
+// Space complexity: O(1)
+
+/**
+ * @param {number[]} nums
+ * @return {number}
+ */
+var missingNumber = function (nums) {
+  const n = nums.length;
+  const target = (n * (n + 1)) / 2;
+
+  const sum = nums.reduce((a, c) => a + c, 0);
+
+  return target - sum;
+};

palindromic-substrings/gwbaik9717.js

@@ -0,0 +1,40 @@
+// Time complexity: O(n^2)
+// Space complexity: O(n^2)
+
+/**
+ * @param {string} s
+ * @return {number}
+ */
+var countSubstrings = function (s) {
+  const n = s.length;
+  const dp = Array.from({ length: n }, () =>
+    Array.from({ length: n }, () => false)
+  );
+  let answer = 0;
+
+  for (let end = 0; end < n; end++) {
+    for (let start = end; start >= 0; start--) {
+      if (start === end) {
+        dp[start][end] = true;
+        answer++;
+        continue;
+      }
+
+      if (start + 1 === end) {
+        if (s[start] === s[end]) {
+          dp[start][end] = true;
+          answer++;
+        }
+        continue;
+      }
+
+      if (s[start] === s[end] && dp[start + 1][end - 1]) {
+        dp[start][end] = true;
+        answer++;
+        continue;
+      }
+    }
+  }
+
+  return answer;
+};

word-search/gwbaik9717.js

@@ -0,0 +1,59 @@
+// h: height of the board, w: width of the board, n: length of the word
+// Time complexity: O(h * w * 4**n)
+// Space complexity: O(n)
+
+/**
+ * @param {character[][]} board
+ * @param {string} word
+ * @return {boolean}
+ */
+var exist = function (board, word) {
+  const n = word.length;
+  const h = board.length;
+  const w = board[0].length;
+
+  const dy = [1, 0, -1, 0];
+  const dx = [0, 1, 0, -1];
+
+  let answer = false;
+
+  const dfs = (current, index) => {
+    if (index === n - 1) {
+      answer = true;
+      return;
+    }
+
+    const [cy, cx] = current;
+    const value = board[cy][cx];
+    board[cy][cx] = "";
+
+    for (let i = 0; i < dy.length; i++) {
+      const ny = cy + dy[i];
+      const nx = cx + dx[i];
+      const ni = index + 1;
+
+      if (
+        ny >= 0 &&
+        ny < h &&
+        nx >= 0 &&
+        nx < w &&
+        board[ny][nx] &&
+        word[ni] === board[ny][nx]
+      ) {
+        dfs([ny, nx], ni);
+      }
+    }
+
+    board[cy][cx] = value;
+  };
+
+  for (let i = 0; i < h; i++) {
+    for (let j = 0; j < w; j++) {
+      if (board[i][j] === word[0] && !answer) {
+        dfs([i, j], 0);
+      }
+    }
+  }
+
+  return answer;
+};