LeetCode第一題：Evaluate Reverse Polish Notation

時間：2014.06.11

地點：基地

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一、題目

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

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二、逆波蘭求值問題，直接上源碼

注意除法不滿足交換律

#include<vector>
#include<stack>
#include<string>
#include<cctype>
#include<iostream>
using namespace std;
class Solution {
public:
	int evalRPN(vector<string> &tokens) {
		stack<int> my_stack_int;
		int lf = 0, rh = 0;
		for (auto& str : tokens)
		{
			if (isdigit(str[0]))
				my_stack_int.push(stoi(str));
			else
			{
				rh = my_stack_int.top();
				my_stack_int.pop();
				lf = my_stack_int.top();
				my_stack_int.pop();
				switch (str[0]){
				case '+':
					lf += rh;break;
				case '-':
					lf -= rh;break;
				case '/':
					lf /= rh;break;
				case '*':
					lf *= rh;break;
				default:
					break;
				}
				my_stack_int.push(lf);
			}
		}
		return my_stack_int.top();
	}
};
int main()
{
	vector<string> str_vec{ "4", "13", "5", "/", "+" };
	Solution sl;
	int a = sl.evalRPN(str_vec);
	cout << a << endl;
}