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.

 

参考：http://www.cnblogs.com/tenosdoit/p/3721918.html

 

C++实现代码：

#include<iostream>

#include<string>

#include<vector>

using namespace std;



class Solution {

public:

    string getPermutation(int n, int k) {

        if(n==0)

            return "";

        int total=factorial(n);

        string str=string("123456789").substr(0,n);

        string ret(n,' ');

        int i;

        for(i=0;i<n;i++)

        {

            int index;

            total=total/(n-i);

            index=(k-1)/total;

            ret[i]=str[index];

            str.erase(index,1);

            k=k-index*total;

        }

        return ret;

    }



    int factorial(int n)

    {

        if(n==0)

            return 0;

        int i;

        int sum=1;

        for(i=1;i<=n;i++)

           sum*=i;

        return sum;

    }

};



int main()

{

    Solution s;

    cout<<s.getPermutation(3,5)<<endl;

}