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):

1. "123"
2. "132"
3. "213"
4. "231"
5. "312"
6. "321"

Given n and k, return the kth permutation sequence.

Note: Given n will be between 1 and 9 inclusive.

输出长度为n的数字串字典序的第K个串。

每一位定下来以后，后面共有(n-1)!个排列，运用这个特点反复减k，让k去逼近1。

class Solution {public:    string getPermutation(int n, int k) {        int mp[10];        mp[0]=mp[1]=1;        vector<int> v(1,1);        for(int i=2;i<10;i++)        {            mp[i]=mp[i-1]*i;            v.push_back(i);        }        string result;        while(n--)        {            vector<int>::iterator it=v.begin();            while(k>mp[n])            {                k-=mp[n];                it++;            }            result+=('0'+*it);            v.erase(it);        }        return result;    }};