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34 lines
853 B
34 lines
853 B
#include <bits/stdc++.h>
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using namespace std;
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int fact[20];
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void init_fact(int n) {
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fact[0] = 1; // 0的阶乘为1
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for (int i = 1; i <= n; i++) fact[i] = fact[i - 1] * i;
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}
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string ans;
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// 逆康托展开
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void getPermutation(int n, int k) {
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vector<char> v; // 存放当前可选数，有序
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for (int i = 1; i <= n; i++) v.push_back(i + '0');
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k--; // 要先 -1 才是其康托展开的值
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for (int i = n; i; i--) {
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int r = k % fact[i - 1];
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int t = k / fact[i - 1];
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k = r;
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ans += v[t]; // 剩余数里第t+1个数为当前位
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v.erase(v.begin() + t); // 移除选做当前位的数
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}
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}
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int main() {
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int n = 5, k = 107; // 107
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init_fact(10); // 预处理阶乘
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getPermutation(n, k);
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cout << ans << endl;
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return 0;
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} |