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45 lines
1.2 KiB
45 lines
1.2 KiB
#include <bits/stdc++.h>
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using namespace std;
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/*
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测试样例：
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+ 23 34
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/ + 4 2 * 3 5
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*/
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// 将前缀表达式转换为后缀表达式(带空格版本)
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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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string prefixToPostfix(string s) {
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stack<string> stk;
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string c; // 子串
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vector<string> q;
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stringstream s1(s); // 构造字符串流，处理带空格的后缀表达式
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while (s1 >> c) q.push_back(c); // 将每个子串抽取出来
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for (int i = q.size() - 1; i >= 0; i--) {
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string c = q[i];
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if (isOp(c)) {
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string a = stk.top();
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stk.pop();
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string b = stk.top();
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stk.pop();
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stk.push(a + " " + b + " " + c);
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} else
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stk.push(c); // 如果是操作数，将其转换为整数并入栈
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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 prefix = "/ + 4 2 * 3 5"; // / + 4 2 * 3 5 --> vector<>={/ + 4 2 * 3 5}
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string postfix = prefixToPostfix(prefix);
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cout << "前缀表达式: " << prefix << endl;
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cout << "后缀表达式: " << postfix << endl;
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return 0;
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} |