添加（0015.三数之和.md）：增加typescript版本

problems/0015.三数之和.md

@@ -332,7 +332,43 @@ var threeSum = function(nums) {
     return res;
 };
 ```
+TypeScript:
 
+```typescript
+function threeSum(nums: number[]): number[][] {
+    nums.sort((a, b) => a - b);
+    let length = nums.length;
+    let left: number = 0,
+        right: number = length - 1;
+    let resArr: number[][] = [];
+    for (let i = 0; i < length; i++) {
+        if (i > 0 && nums[i] === nums[i - 1]) {
+            continue;
+        }
+        left = i + 1;
+        right = length - 1;
+        while (left < right) {
+            let total: number = nums[i] + nums[left] + nums[right];
+            if (total === 0) {
+                resArr.push([nums[i], nums[left], nums[right]]);
+                left++;
+                right--;
+                while (nums[right] === nums[right + 1]) {
+                    right--;
+                }
+                while (nums[left] === nums[left - 1]) {
+                    left++;
+                }
+            } else if (total < 0) {
+                left++;
+            } else {
+                right--;
+            }
+        }
+    }
+    return resArr;
+};
+```
 
 ruby:
 ```ruby