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Update 0150.逆波兰表达式求值.md

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problems/0150.逆波兰表达式求值.md
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@ -89,26 +89,32 @@ C++代码如下：
class Solution { class Solution {
public: public:
int evalRPN(vector<string>& tokens) { int evalRPN(vector<string>& tokens) {
stack<int> st; // 考虑到第20个样例使用int会溢出
// 此处使用long long来存储number
// 在最后用int()强行转换成int输出
stack<long long> st;
for (int i = 0; i < tokens.size(); i++) { for (int i = 0; i < tokens.size(); i++) {
if (tokens[i] == "+" || tokens[i] == "-" || tokens[i] == "*" || tokens[i] == "/") { if (tokens[i] == "+" || tokens[i] == "-" || tokens[i] == "*" || tokens[i] == "/") {
int num1 = st.top(); long long num1 = st.top();
st.pop(); st.pop();
int num2 = st.top(); long long num2 = st.top();
st.pop(); st.pop();
if (tokens[i] == "+") st.push(num2 + num1); if (tokens[i] == "+") st.push(num2 + num1);
if (tokens[i] == "-") st.push(num2 - num1); if (tokens[i] == "-") st.push(num2 - num1);
if (tokens[i] == "*") st.push(num2 * num1); if (tokens[i] == "*") st.push(num2 * num1);
if (tokens[i] == "/") st.push(num2 / num1); if (tokens[i] == "/") st.push(num2 / num1);
} else { } else {
st.push(stoi(tokens[i])); st.push(atoll(tokens[i].c_str()));
} }
} }
int result = st.top();
long long result = st.top();
st.pop(); // 把栈里最后一个元素弹出（其实不弹出也没事） st.pop(); // 把栈里最后一个元素弹出（其实不弹出也没事）
return result; return int(result);
} }
}; };
``` ```
## 题外话 ## 题外话