Create 2179.Count-Good-Triplets-in-an-Array.cpp

Segment_Tree/2179.Count-Good-Triplets-in-an-Array/2179.Count-Good-Triplets-in-an-Array.cpp

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+class BIT{
+    public:
+    int N;    
+    vector<long long>bitArr; // Note: all arrays are 1-index
+    vector<long long>nums;
+    long long M = 1e9+7;
+
+    BIT(int N)
+    {
+        this->N = N;
+        bitArr.resize(N+1);
+        nums.resize(N+1);        
+    }
+
+    // increase nums[i] by delta
+    void updateDelta(int i, long long delta) {
+        int idx = i;
+        while (idx <= N)
+        {
+            bitArr[idx]+=delta;
+            bitArr[idx] %= M;
+            idx+=idx&(-idx);
+        }
+    }
+
+    // sum of a range nums[1:j] inclusively
+    long long queryPreSum(int idx){
+        long long result = 0;
+        while (idx){
+            result += bitArr[idx];
+            result %= M;
+            idx-=idx&(-idx);
+        }
+        return result;
+    }
+
+    // sum of a range nums[i:j] inclusively
+    long long sumRange(int i, int j) {    
+        return queryPreSum(j)-queryPreSum(i-1);
+    } 
+};
+
+class Solution {
+public:    
+    long long goodTriplets(vector<int>& nums1, vector<int>& nums2) 
+    {
+        int n = nums1.size();
+        unordered_map<int,int>Map;
+        for (int i=0; i<n; i++)
+            Map[nums1[i]] = i;
+
+        for (int i=0; i<n; i++)
+            nums2[i] = Map[nums2[i]]+1;
+
+        vector<int>smallerBefore(n,0);
+        BIT bit1(100005);
+        for (int i=0; i<n; i++)
+        {
+            smallerBefore[i] = bit1.sumRange(1,nums2[i]);
+            bit1.updateDelta(nums2[i], 1);
+        }
+
+        vector<int>largerAfter(n,0);
+        BIT bit2(100005);
+        for (int i=n-1; i>=0; i--)
+        {
+            largerAfter[i] = bit2.sumRange(nums2[i], 100000);
+            bit2.updateDelta(nums2[i], 1);
+        }
+
+        long long ret = 0;
+        for (int i=0; i<n; i++)
+            ret += (long long)smallerBefore[i] * (long long)largerAfter[i];
+        return ret;
+    }    
+};