leetcode/code/lc150.java at master · mJackie/leetcode · GitHub

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package code;

* 150. Evaluate Reverse Polish Notation

* 题意：波兰表达式运算

* 难度：Medium

* 分类：Stack

* 思路：用栈即可

* Tips：

import java.util.Stack;

public class lc150 {

public int evalRPN(String[] tokens) {

if(tokens.length==1) return Integer.valueOf(tokens[0]);

Stack<Integer> st = new Stack();

String opration = "+-*/";

int res = 0;

for (int i = 0; i < tokens.length ; i++) {

if(opration.contains(tokens[i])){

int n2 = st.pop(); //注意n1,n2顺序，除法时两个数是有顺序的

int n1 = st.pop();

System.out.println(n1);

System.out.println(n2);

if(tokens[i].equals("+")){ //注意用equeals

res = n1 + n2;

}else if(tokens[i].equals("-")){

res = n1 - n2;

}else if(tokens[i].equals("*")){

res = n1 * n2;

}else if(tokens[i].equals("/")){

res = n1 / n2;

}

st.push(res);

System.out.println(res);

}else{

st.push(Integer.valueOf(tokens[i]));;

}

return res;

}

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