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permutation_sequence.cpp
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42 lines (36 loc) · 885 Bytes
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/*
The set [1,2,3,…,n] contains a total of n! unique permutations.
By listing and labeling all of the permutations in order,
We get the following sequence (ie, for n = 3):
"123"
"132"
"213"
"231"
"312"
"321"
Given n and k, return the kth permutation sequence.
Note: Given n will be between 1 and 9 inclusive.
*/
class Solution {
public:
int factorial(int n) {
int res = 1;
for (int i = 2; i <= n; i++)
res *= i;
return res;
}
string getPermutation(int n, int k) {
string res = "";
for (int i = 1; i <= n; i++)
res += i + '0';
k--;
for (int i = 0; i < n; i++) {
int fac = factorial(n - i - 1);
int x = k / fac;
swap(res[i], res[i + x]);
k = k % fac;
sort(res.begin() + i + 1, res.end());
}
return res;
}
};