77 lines
1.6 KiB
C++
77 lines
1.6 KiB
C++
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#include <cmath>
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#include <iostream>
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#include <stack>
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#include <unordered_map>
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using namespace std;
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unordered_map<char, int> priority{{'(', 0}, {')', 0}, {'+', 1}, {'-', 1},
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{'*', 2}, {'/', 2}, {'^', 3}};
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string in_order2post_order(string src) {
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stack<char> in;
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string builder;
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for (int i = 0; i < src.size(); i++) {
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if (src[i] == ' ')
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continue;
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if (isdigit(src[i]))
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builder += src[i];
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else {
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builder += ' ';
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while (!in.empty() && priority[in.top()] >= priority[src[i]]) {
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builder += in.top();
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in.pop();
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}
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in.push(src[i]);
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}
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}
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if (builder[builder.size() - 1] != ' ')
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builder += ' ';
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while (!in.empty()) {
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builder += in.top();
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in.pop();
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}
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return builder;
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}
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int eval(string src) {
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stack<int> in;
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int num_builder = 0;
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for (int i = 0; i < src.size(); i++) {
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if (isdigit(src[i])) {
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num_builder = num_builder * 10 + src[i] - '0';
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} else if (src[i] == ' ') {
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in.push(num_builder);
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num_builder = 0;
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} else {
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int y = in.top();
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in.pop();
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int x = in.top();
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in.pop();
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switch (src[i]) {
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case '+':
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in.push(x + y);
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break;
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case '-':
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in.push(x - y);
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break;
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case '*':
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in.push(x * y);
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break;
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case '/':
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in.push(x / y);
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break;
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case '^':
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in.push(pow(x, y));
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break;
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}
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}
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}
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return in.top();
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}
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int main() {
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string str;
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getline(cin, str);
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cout << eval(in_order2post_order(str)) << endl;
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}
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