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38 lines
1.1 KiB
38 lines
1.1 KiB
#include <bits/stdc++.h>
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using namespace std;
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// 判断字符是否是操作符
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bool isOp(string c) {
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return c == "+" || c == "-" || c == "*" || c == "/";
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}
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// 后缀表达式求值
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int eval(string s) {
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stack<int> stk; // 后缀表达式求值要使用到一个栈
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// 构造一个字符串流，方便处理带空格的后缀表达式
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stringstream s1(s);
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string c;
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while (s1 >> c) {
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if (isOp(c)) { // 如果是操作数，将其转换为整数并入栈
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int a = stk.top();
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stk.pop();
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int b = stk.top();
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stk.pop();
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if (c == "+") stk.push(b + a);
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if (c == "-") stk.push(b - a);
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if (c == "*") stk.push(b * a);
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if (c == "/") stk.push(b / a);
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} else
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stk.push(stoi(c)); //"24"-->24
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}
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return stk.top();
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}
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int main() {
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string s = "24 9 6 3 / + 5 - * 4 +";
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cout << "answer: " << eval(s) << endl;
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return 0;
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}
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/*
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中缀表达式: (24*(9+6/3-5)+4)
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后缀表达式: 24 9 6 3 / + 5 - * 4 +
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值=148
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*/ |