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060PermutationSequence.cpp
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060PermutationSequence.cpp
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class Solution {
public:
string getPermutation(int n, int k) {
string res = "";
vector<int> nums = {0,1,2,3,4,5,6,7,8,9};
permute(res, nums, n, k);
return res;
}
void permute(string& res, vector<int>& nums, int n, int k) {
if(n == 1) {
res.push_back(nums[1] + '0');
return;
}
int length = 1, tmpn = n;
tmpn--;
while(tmpn != 1) {
length *= tmpn;
tmpn--;
}
int digit = ceil(double(k)/length);
res.push_back(nums[digit] + '0');
nums.erase(nums.begin() + digit);
permute(res, nums, n-1, k-(digit-1)*length);
}
};
//more concise one
class Solution {
public:
string getPermutation(int n, int k) {
string res = "";
string nums = "123456789";
vector<int> f(n, 1);
for(int i = 1; i < n; ++i)
f[i] = f[i-1] * i;
--k; //important!
for(int i = n-1; i >= 0; --i) {
int index = k / f[i];
k %= f[i];
res.push_back(nums[index]);
nums.erase(index, 1);
}
return res;
}
};