LeetCode 60. Permutation Sequence（排列序列）

原题网址：https://leetcode.com/problems/permutation-sequence/

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.
分析规律：通过排列数的迭代求商和求余，得到目标数字。

public class Solution {
public String getPermutation(int n, int k) {
int f = 1;
for(int i=1; i<n; i++) f*=i;
char[] p = new char
;
for(int i=0; i<n; i++) p[i] = (char)('1' + i);
k --;
for(int i=0; i<n && k>0; i++) {
char t = p[i+k/f];
for(int j=i+k/f; j>i; j--) p[j] = p[j-1];
p[i] = t;
k %= f;
f /= (n-1-i);
}
return new String(p);
}
}