Merge pull request youngyangyang04#993 from hutbzc/master

优化150.逆波兰表达式求值中字符串判断逻辑

Author: youngyangyang04

problems/0150.逆波兰表达式求值.md

@@ -133,39 +133,26 @@ public:
 java:
 
 ```Java
-public class EvalRPN {
-
+class Solution {
     public int evalRPN(String[] tokens) {
         Deque<Integer> stack = new LinkedList();
-        for (String token : tokens) {
-            char c = token.charAt(0);
-            if (!isOpe(token)) {
-                stack.addFirst(stoi(token));
-            } else if (c == '+') {
-                stack.push(stack.pop() + stack.pop());
-            } else if (c == '-') {
-                stack.push(- stack.pop() + stack.pop());
-            } else if (c == '*') {
-                stack.push( stack.pop() * stack.pop());
+        for (int i = 0; i < tokens.length; ++i) {
+            if ("+".equals(tokens[i])) {        // leetcode 内置jdk的问题，不能使用==判断字符串是否相等
+                stack.push(stack.pop() + stack.pop());      // 注意 - 和/ 需要特殊处理
+            } else if ("-".equals(tokens[i])) {
+                stack.push(-stack.pop() + stack.pop());
+            } else if ("*".equals(tokens[i])) {
+                stack.push(stack.pop() * stack.pop());
+            } else if ("/".equals(tokens[i])) {
+                int temp1 = stack.pop();
+                int temp2 = stack.pop();
+                stack.push(temp2 / temp1);
             } else {
-                int num1 = stack.pop();
-                int num2 = stack.pop();
-                stack.push( num2/num1);
+                stack.push(Integer.valueOf(tokens[i]));
             }
         }
         return stack.pop();
     }
-    private boolean isOpe(String s) {
-        return s.length() == 1 && s.charAt(0) <'0' || s.charAt(0) >'9';
-    }
-    private int stoi(String s) {
-        return Integer.valueOf(s);
-    }
-
-    public static void main(String[] args) {
-        new EvalRPN().evalRPN(new String[] {"10","6","9","3","+","-11","*","/","*","17","+","5","+"});
-    }
-
 }
 ```