1. Title
Permutation Sequence
2. Http address
https://leetcode.com/problems/permutation-sequence/
3. The question
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.
4. My code (AC)
1 void modifyMin(char min[],int index) 2 { 3 for(int i = index; i < min.length - 1; i++) 4 { 5 min[i] = min[i+1]; 6 } 7 } 8 public String getPermutation(int n, int k) { 9 10 char str [] = new char[n]; 11 char min [] = new char[n]; 12 int base = 1; 13 int layer = n-1; 14 //base = (n-1)! 15 min[0] = ( char ) (1 + '0'); 16 for(int i = 1 ; i <n ; i++) 17 { 18 base *= i; 19 min[i] = (char )(i + '1'); 20 } 21 for(int i = 0 ; i < n; i++) 22 { 23 int index = k / base; 24 if ( k % base == 0) 25 index --; 26 27 // the min permutation 28 if( k == index * base + 1) 29 { 30 str[i] = min[index]; 31 modifyMin(min,index); 32 int jj = 0; 33 for(int j = i + 1; j < n; j++) 34 { 35 str[j] = min[jj++]; 36 } 37 return new String(str); 38 } 39 40 // the max permutation 41 if ( k == (index + 1) *base ) { 42 str[i] = min[index]; 43 modifyMin(min,index); 44 for(int j = i + 1; j < n; j++) 45 { 46 str[j] = min[n-j -1]; 47 } 48 49 return new String(str); 50 } 51 52 str[i] = min[index]; 53 modifyMin(min,index); 54 k -= index * base; 55 56 if (layer >= 2) 57 { 58 base /= layer; 59 layer--; 60 }else{ 61 base = 1; 62 } 63 } 64 return new String(str); 65 }