[Leetcode] 60. 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.

public class Solution {

public String getPermutation(int n, int k) {
StringBuilder sb = new StringBuilder();
boolean[] used = new boolean
;

k = k - 1;
int factor = 1;
for (int i = 1; i < n; i++) {
factor *= i;
}

for (int i = 0; i < n; i++) {
int index = k / factor;
k = k % factor;
for (int j = 0; j < n; j++) {
if (used[j] == false) {
if (index == 0) {
used[j] = true;
sb.append((char) ('0' + j + 1));
break;
} else {
index--;
}
}
}
if (i < n - 1) {
factor = factor / (n - 1 - i);
}
}

return sb.toString();
}
}