Create 2179_Count_Good_Triplet_in_an_Array.java

Author: vishwajeetmishra4

JAVA/2179_Count_Good_Triplet_in_an_Array.java

@@ -0,0 +1,65 @@
+// Problem Number: 2179
+
+// Count Good Triplet in an Array.
+
+class FenwickTree {
+  public FenwickTree(int n) {
+    sums = new int[n + 1];
+  }
+
+  public void add(int i, int delta) {
+    while (i < sums.length) {
+      sums[i] += delta;
+      i += lowbit(i);
+    }
+  }
+
+  public int get(int i) {
+    int sum = 0;
+    while (i > 0) {
+      sum += sums[i];
+      i -= lowbit(i);
+    }
+    return sum;
+  }
+
+  private int[] sums;
+
+  private static int lowbit(int i) {
+    return i & -i;
+  }
+}
+
+class Solution {
+  public long goodTriplets(int[] nums1, int[] nums2) {
+    final int n = nums1.length;
+    long ans = 0;
+    Map<Integer, Integer> numToIndex = new HashMap<>();
+    int[] arr = new int[n];
+    int[] leftSmaller = new int[n];
+    int[] rightLarger = new int[n];
+    FenwickTree tree1 = new FenwickTree(n); 
+    FenwickTree tree2 = new FenwickTree(n); 
+
+    for (int i = 0; i < n; ++i)
+      numToIndex.put(nums1[i], i);
+
+    for (int i = 0; i < n; ++i)
+      arr[i] = numToIndex.get(nums2[i]);
+
+    for (int i = 0; i < n; ++i) {
+      leftSmaller[i] = tree1.get(arr[i]);
+      tree1.add(arr[i] + 1, 1);
+    }
+
+    for (int i = n - 1; i >= 0; --i) {
+      rightLarger[i] = tree2.get(n) - tree2.get(arr[i]);
+      tree2.add(arr[i] + 1, 1);
+    }
+
+    for (int i = 0; i < n; ++i)
+      ans += (long) leftSmaller[i] * rightLarger[i];
+
+    return ans;
+  }
+}