标签：ret log [] 运算 ack div res span 一个
leetcode 逆波兰式求解
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
import java.util.Stack; public class Solution { public int evalRPN(String[] tokens) { Stack<Integer> stack = new Stack<Integer>(); int tmp; for(int i = 0; i<tokens.length; i++){ if("+".equals(tokens[i])){ int a = stack.pop(); int b = stack.pop(); stack.add(b+a); } else if("-".equals(tokens[i])){ int a = stack.pop(); int b = stack.pop(); stack.add(b-a); } else if("*".equals(tokens[i])){ int a = stack.pop(); int b = stack.pop(); stack.add(b*a); } else if("/".equals(tokens[i])){ int a = stack.pop(); int b = stack.pop(); stack.add(b/a); } else{ stack.add(Integer.parseInt(tokens[i])); } } return stack.pop(); } }
根据你波兰式求值。看到逆波兰式可以想到栈，扫描表达式，遇到数字则将数字入栈，遇到运算符，时，则从栈顶弹出两个元素，后弹出的元素在运算符的左边，先弹出的元素在元素符的右边，执行运算，将结果入栈。扫描结束后，栈中的元素只剩下一个，即逆波兰式的值
leetcode-Evaluate the value of an arithmetic expression in Reverse Polish Notation
标签：ret log [] 运算 ack div res span 一个
原文地址：http://www.cnblogs.com/qj4d/p/7078478.html
