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 for n = 3:
"123"
"132"
"213"
"231"
"312"
"321"
Given n and k, return the kth permutation sequence.
Note:
- Given n will be between 1 and 9 inclusive.
- Given k will be between 1 and n! inclusive.
Example 1:
Input: n = 3, k = 3
Output: "213"
Example 2:
Input: n = 4, k = 9
Output: "2314"
题解:
每次获取当前的首数字,直到最后一个数字。
class Solution {
public:
string getPermutation(int n, int k) {
vector<int> total(n + 1, 1);
vector<char> num;
string res;
for (int i = 1; i <= n; i++) {
num.push_back(i + 48);
}
for (int i = 2; i <= n; i++) {
total[i] = total[i - 1] * i;
}
for (int i = n; i > 0; i--) {
int temp = (k - 1) / total[i - 1];
res += num[temp];
num.erase(num.begin() + temp);
k -= temp * total[i - 1];
}
return res;
}
};