标签：blog http io ar sp java for div on
Evaluate the value of an arithmetic expression in Reverse Polish Notation.
Valid operators are +, -, *, /. Each operand may be an integer or another expression.
Some examples:
["2", "1", "+", "3", "*"] -> ((2 + 1) * 3) -> 9 ["4", "13", "5", "/", "+"] -> (4 + (13 / 5)) -> 6
1,放在堆里面做，碰到符号类就pop 两个数
2，记得输入可能有负数的情况，
tokens[i].matches("-?\\d+")
3，string 不能用＝＝ 必须采用equal
public class Solution {
public int evalRPN(String[] tokens) {
Stack<Integer> store=new Stack<Integer>();
int sum=0;
for(int i=0;i<tokens.length;i++){
if(!tokens[i].matches("-?\\d+")){
int a=store.pop();
int b=store.pop();
if(tokens[i].equals("+")){
sum=b+a;
}
else if(tokens[i].equals("-")){
sum=b-a;
}
else if(tokens[i].equals("*")){
sum=b*a;
}
else if(tokens[i].equals("/")){
sum=b/a;
}
store.push(sum);
}
else{
store.push(Integer.parseInt(tokens[i]));
}
}
return store.pop();
}
}
leetcode Evaluate Reverse Polish Notation
标签：blog http io ar sp java for div on
原文地址：http://www.cnblogs.com/lilyfindjobs/p/4098790.html
