[ganu] Week3

combination-sum/gwbaik9717.js

@@ -0,0 +1,32 @@
+/**
+ * @param {number[]} candidates
+ * @param {number} target
+ * @return {number[][]}
+ */
+var combinationSum = function (candidates, target) {
+  const answer = [];
+  const n = candidates.length;
+  const combi = (i, sum, arr) => {
+    for (let j = i; j < n; j++) {
+      const candidate = candidates[j];
+      const newSum = sum + candidate;
+
+      if (newSum === target) {
+        answer.push([...arr, candidate]);
+        continue;
+      }
+
+      if (newSum > target) {
+        continue;
+      }
+
+      if (newSum < target) {
+        combi(j, newSum, [...arr, candidate]);
+      }
+    }
+  };
+
+  combi(0, 0, []);
+
+  return answer;
+};

maximum-subarray/gwbaik9717.js

@@ -0,0 +1,25 @@
+// Time complexity: O(n)
+// Space complexity: O(1)
+
+/**
+ * @param {number[]} nums
+ * @return {number}
+ */
+var maxSubArray = function (nums) {
+  const n = nums.length;
+  const dp = [0, 0];
+
+  let answer = Number.MIN_SAFE_INTEGER;
+
+  for (let i = 1; i <= n; i++) {
+    if (i % 2 !== 0) {
+      dp[1] = Math.max(dp[0] + nums[i - 1], nums[i - 1]);
+      answer = Math.max(answer, dp[1]);
+    } else {
+      dp[0] = Math.max(dp[1] + nums[i - 1], nums[i - 1]);
+      answer = Math.max(answer, dp[0]);
+    }
+  }
+
+  return answer;
+};

product-of-array-except-self/gwbaik9717.js

@@ -0,0 +1,24 @@
+// Time complexity: O(n)
+// Space complexity: O(n)
+
+/**
+ * @param {number[]} nums
+ * @return {number[]}
+ */
+var productExceptSelf = function (nums) {
+  const n = nums.length;
+  const fromLeft = Array.from({ length: n + 1 }, () => 1);
+  const fromRight = Array.from({ length: n + 1 }, () => 1);
+
+  for (let i = 1; i <= n; i++) {
+    fromLeft[i] = fromLeft[i - 1] * nums[i - 1];
+  }
+
+  for (let i = n - 1; i >= 0; i--) {
+    fromRight[i] = fromRight[i + 1] * nums[i];
+  }
+
+  return nums.map((num, i) => {
+    return fromLeft[i] * fromRight[i + 1];
+  });
+};

reverse-bits/gwbaik9717.js

@@ -0,0 +1,25 @@
+// Time complexity: O(1)
+// Space complexity: O(1)
+
+/**
+ * @param {number} n - a positive integer
+ * @return {number} - a positive integer
+ */
+var reverseBits = function (n) {
+  const stack = [];
+  let current = n;
+
+  for (let i = 0; i < 32; i++) {
+    stack.push(current % 2);
+    current = Math.floor(current / 2);
+  }
+
+  let answer = 0;
+
+  for (let i = 0; i < 32; i++) {
+    const popped = stack.pop();
+    answer += popped * 2 ** i;
+  }
+
+  return answer;
+};

two-sum/gwbaik9717.js

@@ -0,0 +1,22 @@
+// Time complexity: O(n)
+// Space complexity: O(n)
+
+/**
+ * @param {number[]} nums
+ * @param {number} target
+ * @return {number[]}
+ */
+var twoSum = function (nums, target) {
+  const map = new Map();
+
+  for (let i = 0; i < nums.length; i++) {
+    const num = nums[i];
+    const diff = target - num;
+
+    if (map.has(diff)) {
+      return [i, map.get(diff)];
+    } else {
+      map.set(num, i);
+    }
+  }
+};