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LeetCode: Reverse Words in a String:Evaluate Reverse Polish Notation
LeetCode: Reverse Words in a String:Evaluate Reverse Polish Notation
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
地址:https://oj.leetcode.com/problems/evaluate-reverse-polish-notation/
计算波兰后缀表达式的值,具体做法是利用一个栈,如果遇到数字则把数字进栈,如果遇到操作符就把栈中的数字出栈进行运算(二元操作符出栈两个数字,一元操作符出栈一个数字),最后的结果存在栈中。代码:
1 class Solution { 2 public: 3 int evalRPN(vector<string> &tokens) { 4 int lop, rop; 5 vector<string>::const_iterator cIter = tokens.begin(); 6 stack<int> s; 7 for(; cIter != tokens.end(); ++cIter){ 8 if ((*cIter).size() == 1 && !isdigit((*cIter)[0])){ 9 char op = (*cIter)[0];10 rop = s.top();11 s.pop();12 lop = s.top();13 s.pop();14 if (‘+‘ == op){15 s.push(lop + rop);16 } else if (‘-‘ == op){17 s.push(lop - rop);18 } else if (‘*‘ == op){19 s.push(lop * rop);20 } else{21 s.push(lop / rop);22 }23 } else {24 s.push(atoi((*cIter).c_str()));25 }26 }27 return s.top();28 }29 };
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