Create 0018-4sum.ts

Author: andynullwong

Diff for: typescript/0018-4sum.ts

@@ -0,0 +1,43 @@
+function fourSum(nums: number[], target: number): number[][] {
+    const sortedNums: number[] = nums.sort((a: number, b: number) => a - b);
+    const res: number[][] = [];
+    const quad: number[] = [];
+
+    const kSum = (k: number, start: number, target: number): void => {
+        if (k > 2) {
+            for (let i = start; i < sortedNums.length; i++) {
+                if (i !== start && sortedNums[i] === sortedNums[i - 1]) {
+                    continue;
+                }
+                quad.push(sortedNums[i]);
+                kSum(k - 1, i + 1, target - sortedNums[i]);
+                quad.pop();
+            }
+        } else {
+            let left: number = start;
+            let right: number = sortedNums.length - 1;
+
+            while (left < right) {
+                const sum = sortedNums[left] + sortedNums[right];
+                if (sum < target) {
+                    left++;
+                } else if (sum > target) {
+                    right--;
+                } else {
+                    res.push(
+                        quad.concat([sortedNums[left], sortedNums[right]])
+                    );
+                    left++;
+                    while (
+                        left < right &&
+                        sortedNums[left] === sortedNums[left - 1]
+                    ) {
+                        left++;
+                    }
+                }
+            }
+        }
+    };
+    kSum(4, 0, target);
+    return res;
+}