Create 3404.Count-Special-Subsequences.cpp

Author: wisdompeak

Others/3404.Count-Special-Subsequences/3404.Count-Special-Subsequences.cpp

@@ -0,0 +1,32 @@
+using LL = long long;
+class Solution {
+public:
+ LL getKey(int x, int y)
+ {
+ int g = gcd(x,y);
+ x = x/g;
+ y = y/g;
+ return (LL)x*1000+y;
+ }
+ long long numberOfSubsequences(vector<int>& nums) 
+ {
+ unordered_map<LL, vector<int>>Map;
+ int n = nums.size();
+ for (int i=0; i<n; i++)
+ for (int j=i+2; j<n; j++) 
+ Map[getKey(nums[i], nums[j])].push_back(j); 
+ 
+ for (auto& [k,v]:Map)
+ sort(v.begin(), v.end());
+ 
+ LL ret = 0;
+ for (int r=2; r<n; r++)
+ for (int s=r+2; s<n; s++)
+ {
+ int key = getKey(nums[s], nums[r]); 
+ auto iter = lower_bound(Map[key].begin(), Map[key].end(), r-1);
+ ret += iter - Map[key].begin();
+ }
+ return ret;
+ }
+};