0150.逆波兰表达式求值 添加更快速的python解

problems/0150.逆波兰表达式求值.md

@@ -163,6 +163,25 @@ class Solution {
 
 python3
 
+```python
+from operator import add, sub, mul
+
+class Solution:
+    op_map = {'+': add, '-': sub, '*': mul, '/': lambda x, y: int(x / y)}
+
+    def evalRPN(self, tokens: List[str]) -> int:
+        stack = []
+        for token in tokens:
+            if token not in {'+', '-', '*', '/'}:
+                stack.append(int(token))
+            else:
+                op2 = stack.pop()
+                op1 = stack.pop()
+                stack.append(self.op_map[token](op1, op2))  # 第一个出来的在运算符后面
+        return stack.pop()
+```
+
+另一种可行，但因为使用eval相对较慢的方法:
 ```python
 class Solution:
     def evalRPN(self, tokens: List[str]) -> int: