LeetCode 150. Evaluate Reverse Polish Notation
Solution1:
参考网址:http://www.cnblogs.com/grandyang/p/4247718.html
这道题果然应该是栈的完美应用啊,从前往后遍历数组,遇到数字则压入栈中,遇到符号,则把栈顶的两个数字拿出来运算,把结果再压入栈中,直到遍历完整个数组,栈顶数字即为最终答案。代码如下:
class Solution {
public:
int evalRPN(vector<string> &tokens) {
if (tokens.size() == 1) return atoi(tokens[0].c_str());
stack<int> s;
for (int i = 0; i < tokens.size(); ++i) {
if (tokens[i] != "+" && tokens[i] != "-" && tokens[i] != "*" && tokens[i] != "/")
{
s.push(atoi(tokens[i].c_str()));
} else {
int m = s.top();
s.pop();
int n = s.top();
s.pop();
if (tokens[i] == "+") s.push(n + m);
if (tokens[i] == "-") s.push(n - m);
if (tokens[i] == "*") s.push(n * m);
if (tokens[i] == "/") s.push(n / m);
}
}
return s.top();
}
};