**LeetCode 60. Permutation Sequence

https://leetcode.com/problems/permutation-sequence/

康拓展开和逆康拓展开

自己推一推  参考http://www.cnblogs.com/hxsyl/archive/2012/04/11/2443009.html

class Solution {
public:
    string getPermutation(int n, int k) {
        k--;
        for(int i=0;i<=n;i++){
            vis[i]=0;
            if(i == 0)jie[i]=1;
            else jie[i] = (i)*jie[i-1];
        }

        string ret;
        for(int i=n-1;i>0;i--) {
            int div = k/jie[i];
            int mod = k%jie[i];
            ret = ret + getDiv(div+1,n);
            //cout << "div=" << div << "  " << "  mod=" << mod << endl;
            k = mod;
        }
        for(int i=1;i<=n;i++)
            if(!vis[i])
                ret = ret + (char)(i+'0');
        return ret;
    }

    char getDiv(int d, int n) {
        int cnt=0;
        for(int i=1;i<=n;i++) {

            if(!vis[i]) {
                cnt++;
                if( cnt == d ) {
                    vis[i] = 1;
                    return (char)(i+'0');
                }
            }
        }
        return '0';
    }
private:
    int vis[10], jie[10];
};