Merge pull request #1049 from xiaofei-2020/stack4

添加（0020.有效的括号.md）：增加typescript版本

problems/0020.有效的括号.md

@@ -283,8 +283,60 @@ var isValid = function(s) {
 };
 ```
 
+TypeScript:
+
+版本一：普通版
+
+```typescript
+function isValid(s: string): boolean {
+    let helperStack: string[] = [];
+    for (let i = 0, length = s.length; i < length; i++) {
+        let x: string = s[i];
+        switch (x) {
+            case '(':
+                helperStack.push(')');
+                break;
+            case '[':
+                helperStack.push(']');
+                break;
+            case '{':
+                helperStack.push('}');
+                break;
+            default:
+                if (helperStack.pop() !== x) return false;
+                break;
+        }
+    }
+    return helperStack.length === 0;
+};
+```
+
+版本二：优化版
+
+```typescript
+function isValid(s: string): boolean {
+    type BracketMap = {
+        [index: string]: string;
+    }
+    let helperStack: string[] = [];
+    let bracketMap: BracketMap = {
+        '(': ')',
+        '[': ']',
+        '{': '}'
+    }
+    for (let i of s) {
+        if (bracketMap.hasOwnProperty(i)) {
+            helperStack.push(bracketMap[i]);
+        } else if (i !== helperStack.pop()) {
+            return false;
+        }
+    }
+    return helperStack.length === 0;
+};
+```
 
 Swift
+
 ```swift
 func isValid(_ s: String) -> Bool {
     var stack = [String.Element]()