标签：style blog color 使用 io strong for div cti
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):
Given n and k, return the kth permutation sequence.
Note: Given n will be between 1 and 9 inclusive.
思路：使用标准库函数next_permutation循环k-1次求解将会超时。对于最高位n，其取值每加1，对应增加(n-1)!个排列实例。于是，对于给定的k，最高位的取值应为：(k-1) / (n-1)!。因此，可以考虑从高往低逐位确定每一位的取值。
1 class Solution { 2 public: 3 string getPermutation( int n, int k ) { 4 int factorial = n; 5 string permutation, selection( n, ‘1‘ ); 6 for( int i = 1; i < n; ++i ) { 7 factorial *= i; 8 selection[i] += i; 9 } 10 for( int i = 0; i < n && k > 0; ++i ) { 11 factorial /= (n-i); 12 int select = (k-1) / factorial; 13 k %= factorial; 14 permutation.push_back( selection[select] ); 15 selection.erase( select, 1 ); 16 } 17 permutation.insert( permutation.end(), selection.rbegin(), selection.rend() ); 18 return permutation; 19 } 20 };
标签：style blog color 使用 io strong for div cti
原文地址：http://www.cnblogs.com/moderate-fish/p/3935714.html
