LeetCode刷题记录 - 60.第k个排列

执行用时：4ms

语言：cpp

思路：和求十进制数各位数类似，用k/(n-1)!判断每一位是该位的第几轮排列，再让k%(n-1)!计算下一位

代码：

class Solution {
public:
    string getPermutation(int n, int k) {
        int m = fac(n);
        string res = "";
        vector<int> tb;
        
        for(int i = 1;i <= n;i++){
            tb.push_back(i);
        }
        
        int i = n -1;
        k--;
        
        while(i > 0){
            int t = fac(i);
            int j = k / t;
            
            char c = (tb[j] + '0');
            res += c;
            
            tb.erase(tb.begin()+j);
            k %= t;
            i--;
        }
        
        res += (tb[0] + '0');
        return res;
    }
    
private:
    int fac(int n){
        int res = 1;
        for(int i = 2;i <= n;i++){
            res *= i;
        }
        return res;
    }
};