Update 18-4sum.js

Author: everthis

18-4sum.js

@@ -1,3 +1,49 @@
+/**
+ * @param {number[]} nums
+ * @param {number} target
+ * @return {number[][]}
+ */
+const fourSum = function (nums, target) {
+  nums.sort((a, b) => a - b)
+  const results = []
+  kSum(nums, target, 4, 0, [], results)
+  return results
+}
+
+function kSum(nums, target, k, i, acc, results) {
+  if (nums[i] * k > target || nums[nums.length - 1] * k < target) return
+  if (k > 2) {
+    for (let j = i; j <= nums.length - k; j++) {
+      if (j == i || nums[j] > nums[j - 1])
+        kSum(nums, target - nums[j], k - 1, j + 1, [...acc, nums[j]], results)
+    }
+  } else {
+    twoSum(nums, target, i, acc, results)
+  }
+}
+
+function twoSum(nums, target, i, acc, results) {
+  let lo = i
+  let hi = nums.length - 1
+  while (lo < hi) {
+    const sum = nums[lo] + nums[hi]
+    if (sum == target) {
+      results.push([...acc, nums[lo], nums[hi]])
+      while (nums[lo] == nums[lo + 1]) lo++
+      while (nums[hi] == nums[hi - 1]) hi--
+      lo++
+      hi--
+    } else if (sum < target) {
+      lo++
+    } else {
+      hi--
+    }
+  }
+}
+
+
+// another
+
 /**
  * @param {number[]} nums
  * @param {number} target