996. Number of Squareful Arrays
An array is squareful if the sum of every pair of adjacent elements is a perfect square.
Given an integer array nums, return the number of permutations of nums that are squareful.
Two permutations perm1 and perm2 are different if there is some index i such that perm1[i] != perm2[i].
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| class Solution {
unordered_map<int, int> counter;
unordered_map<int, vector<int>> ref;
int backTracking(int n, int pick) {
if(!pick) return 1;
int res = 0;
for(auto r : ref[n]) {
if(counter[r]) {
counter[r]--;
res += backTracking(r, pick - 1);
counter[r]++;
}
}
return res;
}
public:
int numSquarefulPerms(vector<int>& nums) {
for(auto n : nums) counter[n]++;
for(auto [i, _] : counter) {
for(auto [j, _]: counter) {
int sum = i + j, sq = sqrt(i + j);
if(sum == sq * sq) {
ref[i].push_back(j);
}
}
}
int res = 0;
for(auto [n, _]: counter) {
counter[n]--;
res += backTracking(n, nums.size() - 1);
counter[n]++;
}
return res;
}
};
|
