Create 2179. Count Good Triplets in an Array (#768)

Author: Chayandas07

2179. Count Good Triplets in an Array

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+class Solution 
+{
+public:
+    using ll = long long;
+    vector<ll> bit1, bit2;
+    int n;
+    void update(vector<ll>& bit, int i, ll val) 
+    {
+        for (++i; i <= n; i += (i & -i))
+            bit[i] += val;
+    }
+    ll query(const vector<ll>& bit, int i) 
+    {
+        ll res = 0;
+        for (++i; i > 0; i -= (i & -i))
+            res += bit[i];
+        return res;
+    }
+    long long goodTriplets(vector<int>& nums1, vector<int>& nums2) 
+    {
+        n = nums1.size();
+        vector<int> pos(n);
+        for (int i = 0; i < n; ++i)
+            pos[nums2[i]] = i;
+        for (int i = 0; i < n; ++i)
+            nums1[i] = pos[nums1[i]];
+        bit1.assign(n + 2, 0);
+        bit2.assign(n + 2, 0);
+        ll ans = 0;
+        for (int i = n - 1; i >= 0; --i) 
+        {
+            int x = nums1[i];
+            ll val = query(bit1, n - 1) - query(bit1, x);
+            ll trip = query(bit2, n - 1) - query(bit2, x);
+            ans += trip;
+            update(bit2, x, val);
+            update(bit1, x, 1);
+        }
+        return ans;
+    }
+};