LeetCode Evaluate Reverse Polish Notation

最新推荐文章于 2019-04-05 17:47:30 发布

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本文介绍了一种解决逆波兰表达式求值问题的方法。利用栈数据结构处理加减乘除运算，通过遍历字符串数组解析表达式并计算结果。示例展示了如何使用此方法求得逆波兰表达式的值。

题目：

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

class Solution {
public:
    int evalRPN(vector<string> &tokens) {
    	stack<int> oped;
    	for(auto it : tokens) {
    		//数字，进栈 
    		if(isdigit(it[0]) || it.size() > 1) {
    			oped.push(atoi(it.c_str()));	
    		} 
    		//出栈两个数，计算后入栈 
    		else {
    			int oped2 = oped.top();
				oped.pop();
				int oped1 = oped.top();
				oped.pop();
				switch (it[0]) {
					case '+':
						oped.push(oped1+oped2);
						break;
					case '-':
						oped.push(oped1-oped2);
						break;
					case '*':
						oped.push(oped1*oped2);
						break;
					case '/':
						oped.push(oped1/oped2);
						break;
				}	
    		}	
    	}
    	return oped.top();      
    }
};