添加（0078.子集.md）：增加typescript版本

problems/0078.子集.md

@@ -272,7 +272,28 @@ var subsets = function(nums) {
 };
 ```
 
+## TypeScript
+
+```typescript
+function subsets(nums: number[]): number[][] {
+    const resArr: number[][] = [];
+    backTracking(nums, 0, []);
+    return resArr;
+    function backTracking(nums: number[], startIndex: number, route: number[]): void {
+        resArr.push(route.slice());
+        let length = nums.length;
+        if (startIndex === length) return;
+        for (let i = startIndex; i < length; i++) {
+            route.push(nums[i]);
+            backTracking(nums, i + 1, route);
+            route.pop();
+        }
+    }
+};
+```
+
 ## C
+
 ```c
 int* path;
 int pathTop;