Merge pull request #1052 from xiaofei-2020/stack6

添加（0150.逆波兰表达式求值.md）：增加typescript版本

problems/0150.逆波兰表达式求值.md

@@ -210,6 +210,71 @@ var evalRPN = function(tokens) {
 };
 ```
 
+TypeScript：
+
+普通版：
+
+```typescript
+function evalRPN(tokens: string[]): number {
+    let helperStack: number[] = [];
+    let temp: number;
+    let i: number = 0;
+    while (i < tokens.length) {
+        let t: string = tokens[i];
+        switch (t) {
+            case '+':
+                temp = helperStack.pop()! + helperStack.pop()!;
+                helperStack.push(temp);
+                break;
+            case '-':
+                temp = helperStack.pop()!;
+                temp = helperStack.pop()! - temp;
+                helperStack.push(temp);
+                break;
+            case '*':
+                temp = helperStack.pop()! * helperStack.pop()!;
+                helperStack.push(temp);
+                break;
+            case '/':
+                temp = helperStack.pop()!;
+                temp = Math.trunc(helperStack.pop()! / temp);
+                helperStack.push(temp);
+                break;
+            default:
+                helperStack.push(Number(t));
+                break;
+        }
+        i++;
+    }
+    return helperStack.pop()!;
+};
+```
+
+优化版：
+
+```typescript
+function evalRPN(tokens: string[]): number {
+    const helperStack: number[] = [];
+    const operatorMap: Map<string, (a: number, b: number) => number> = new Map([
+        ['+', (a, b) => a + b],
+        ['-', (a, b) => a - b],
+        ['/', (a, b) => Math.trunc(a / b)],
+        ['*', (a, b) => a * b],
+    ]);
+    let a: number, b: number;
+    for (let t of tokens) {
+        if (operatorMap.has(t)) {
+            b = helperStack.pop()!;
+            a = helperStack.pop()!;
+            helperStack.push(operatorMap.get(t)!(a, b));
+        } else {
+            helperStack.push(Number(t));
+        }
+    }
+    return helperStack.pop()!;
+};
+```
+
 python3
 
 ```python