week3 solutions (#2735)

Author: jthw1005

combination-sum/jthw1005.js

@@ -0,0 +1,12 @@
+function combinationSum(candidates, target) {
+  const dp = Array.from({ length: target + 1 }, () => []);
+  dp[0] = [[]];
+  for (let i = 0; i < candidates.length; i++) {
+    for (let j = candidates[i]; j <= target; j++) {
+      dp[j].push(
+        ...dp[j - candidates[i]].map((item) => [...item, candidates[i]]),
+      );
+    }
+  }
+  return dp[target];
+}

decode-ways/jthw1005.js

@@ -0,0 +1,16 @@
+function numDecodings(s) {
+  const dp = Array.from({ length: s.length + 1 }, () => 0);
+  dp[0] = 1;
+  dp[1] = s[0] === '0' ? 0 : 1;
+  for (let i = 2; i <= s.length; i++) {
+    if (s[i - 1] !== '0') {
+      dp[i] += dp[i - 1];
+    }
+
+    const twoDigits = Number(s.slice(i - 2, i));
+    if (twoDigits >= 10 && twoDigits <= 26) {
+      dp[i] += dp[i - 2];
+    }
+  }
+  return dp[s.length];
+}

maximum-subarray/jthw1005.js

@@ -0,0 +1,9 @@
+function maxSubArray(nums) {
+  let max = nums[0];
+  let current = nums[0];
+  for (let i = 1; i < nums.length; i++) {
+    current = Math.max(nums[i], current + nums[i]);
+    max = Math.max(max, current);
+  }
+  return max;
+}

number-of-1-bits/jthw1005.js

@@ -0,0 +1,6 @@
+function hammingWeight(n) {
+  return n
+    .toString(2)
+    .split('')
+    .filter((v) => v === '1').length;
+}

valid-palindrome/jthw1005.js

@@ -0,0 +1,4 @@
+function isPalindrome(s) {
+  const letters = s.replace(/[^a-zA-Z0-9]/g, '').toLowerCase();
+  return letters === letters.split('').reverse().join('');
+}