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100 lines
2.3 KiB
100 lines
2.3 KiB
#include <bits/stdc++.h>
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using namespace std;
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string s;
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//栈：数字
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stack<int> f;
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//栈：操作符
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stack<char> symbol;
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//操作符之间的优先级的比较
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char cmp(char a, char b) {
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//右括号不会进栈，不必写右括号的优先级
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//遇到右括号就弹出左括号
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if (a == '#') {
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if (b == '#') {
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return '=';
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} else {
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return '<';
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}
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}
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if (a == '+' || a == '-') {
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if (b == '*' || b == '/' || b == '(') {
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return '<';
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} else {
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return '>';
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}
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}
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if (a == '*' || a == '/') {
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if (b == '(') {
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return '<';
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} else {
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return '>';
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}
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}
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if (a == '(') {
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if (b == ')') {
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return '=';
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} else {
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return '<';
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}
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}
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}
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//返回计算结果
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int cal(int a, int b, char op) {
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switch (op) {
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case '+':
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return a + b;
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case '-':
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return a - b;
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case '*':
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return a * b;
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case '/':
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return a / b;
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}
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}
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//表达式计算的过程
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int process() {
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int i = 0, num = 0;
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while (symbol.top() != '#' || i < s.size()) {
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if (s[i] >= '0' && s[i] <= '9') {
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//为操作数
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num = 0;
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while (s[i] >= '0' && s[i] <= '9') {
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num *= 10;
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num += s[i] - '0';
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++i;
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}
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f.push(num);
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} else {
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switch (cmp(symbol.top(), s[i])) {
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case '<':
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symbol.push(s[i]);
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++i;
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break;
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case '=':
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symbol.pop();
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++i;
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break;
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case '>':
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int a = f.top();
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f.pop();
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int b = f.top();
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f.pop();
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f.push(cal(b, a, symbol.top()));
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symbol.pop();
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break;
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}
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}
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}
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int res = f.top();
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f.pop();
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return res;
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}
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int main() {
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symbol.push('#');
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//测试用例： 2*(2+3)-4
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s = "2*(2+3)-4";
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cout << s << "=" << process() << endl;
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return 0;
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} |