Evaluate the value of arithmetic expression in Reverse Polish Notation. Valid operator are ,-,*,/. Each operand may be an integer or another expression. Some examples: [2, 1, , 3, *] – ((21)*3) – 9 [4, 13, 5, /, ] – (本文来源gao($daima.com搞@代@#码8网^4 (13 / 5)) – 6 分析：
Evaluate the value of arithmetic expression in Reverse Polish Notation.
Valid operator 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
分析：后缀表达式操作。
栈的应用，如果碰见数字，则压栈，碰见运算符则弹出两个元素，对两个元素进行数学运算后结果压栈。
public class Solution { public int evalRPN(String[] tokens) { Stack st = new Stack(); for(String token : tokens){ if(token.matches("-?[0-9]+")){ st.push(Integer.parseInt(token)); }else{ int num2 = st.pop(); int num1 = st.pop(); if(token.equals("+")){ st.push(num1+num2); }else if(token.equals("-")){ st.push(num1-num2); }else if(token.equals("*")){ st.push(num1*num2); }else if(token.equals("/")){ st.push(num1/num2); } } } return st.pop(); }}
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转载请注明原文链接：LeetCode 2 Evaluate Reverse Polish Notation
转载请注明原文链接：LeetCode 2 Evaluate Reverse Polish Notation
