53 lines
1.3 KiB
C++
53 lines
1.3 KiB
C++
#include <bits/stdc++.h>
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using namespace std;
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#define str to_string //利用define缩短代码
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vector<string> path;
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const int N = 30;
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int a[N];
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void dfs(int step, int res) {
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if (step == 4) {
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if (res == 24) {
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for (int i = 0; i < path.size(); i++, puts("")) printf("%d", path[i]);
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exit(0);
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}
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return;
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}
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int x = a[step];
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if (x > res) swap(x, res);
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path.push_back(str(res) + "+" + str(x) + "=" + str(res + x));
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dfs(step + 1, res + x);
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path.pop_back();
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path.push_back(str(res) + "-" + str(x) + "=" + str(res - x));
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dfs(step + 1, res - x);
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path.pop_back();
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path.push_back(str(res) + "*" + str(x) + "=" + str(res * x));
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dfs(step + 1, res * x);
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path.pop_back();
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if (x && res % x == 0) {
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path.push_back(str(res) + "/" + str(x) + "=" + str(res / x));
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dfs(step + 1, res / x);
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path.pop_back();
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}
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}
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int main() {
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for (int i = 0; i < 4; i++) scanf("%d", &a[i]);
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do {
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dfs(1, a[0]);
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} while (next_permutation(a, a + 4));
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puts("No answer!");
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return 0;
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}
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/*
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考虑添加括号的情况，假设**?**为运算符，一共只有5种：
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1.((a?b)?c)?d
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2.(a?(b?c))?d
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3.a?((b?c)?d)
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4.(a?b)?(c?d)
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5.a?(b?(c?d))
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*/ |