Help me understand this part. Which two pointer pattern is this? Where to learn more topics like this?

for (int i = 1, j = 1; i <= n; i = j) {
      for (j = i + 1; j <= n and a[i] == a[j]; j++);
      int k = (j - i);
      ans -= 1LL * k * (k + 1) / 2;
    }

Counting the number of subarrays which have the same elements is pretty easy. Let r be the rightmost index such that a[l] = a[l + 1] = ... = a[r] . Then the number of subarrays having the same elements will be $$$\frac{(r - l + 1) \cdot (r - l + 2)}{2}$$$. Do similar thing for other elements too. Check out the code to understand better.

https://bangladesh-cp-server.notion.site/ICPC-Preliminary-2023-Editorial-37171693c196474298daae73812c8d51

#include<bits/stdc++.h>
using namespace std;

int32_t main() {
  ios_base::sync_with_stdio(0);
  cin.tie(0);
  int t, cs = 0; cin >> t;
  while (t--) {
    int n; cin >> n;
    int a[n + 1];
    for (int i = 1; i <= n; i++) {
      cin >> a[i];
    }
    long long ans = 1LL * n * (n + 1) / 2;
    for (int i = 1, j = 1; i <= n; i = j) {
      for (j = i + 1; j <= n and a[i] == a[j]; j++);
      int k = (j - i);
      ans -= 1LL * k * (k + 1) / 2;
    }
    cout << "Case " << ++cs << ": " << ans << '\n';
  }
  return 0;
}

Correct answer in sample case. But I get wrong answer in [1,2,3] answer = 2 how to fix this?

long long cnt= 1, BeautifulArray = 1;
    for (int i = 0; i < n - 1; i++) {
      if (a[i] == a[i + 1]) {
        cnt++;
      } else {
        BeautifulArray += (cnt * (cnt + 1) / 2);
        cnt = 1;
      }
    }
answer = totalSubarray - BeautifulArray;

Problem E Sub-Array

An array is Beautiful if all the elements in that array are identical.

You are given an array A consists of N integers. Now for the given array, you have to find the number of non-empty subarrays which are not Beautiful.

A subarray is a contiguous part of the array.

Example: A = [ 1, 0, 1, 0 ] where N = 4 Possible six subarrays which aren’t beautiful. [1,0] , [1,0,1] , [1,0,1,0] , [0,1] , [0,1,0] , [1,0]

Input Input starts with an integer T denoting the number of test cases. Each case starts with an T integer N denoting the number of integers in the array. Next line will contain N integers of array A, separated by spaces.

Output For each case, print the case number and the result in a single line.

Constraints: ● 1 ≤ T ≤ 10 ● 1 ≤ N ≤ 10^5 ● 0 ≤ A[i] ≤ 2^31-1

Sample Input

2
4
1 0 1 0
7
1 1 2 3 3 4 7

Output for Sample Input

Case 1: 6
Case 2: 19

Update: Give me a hint please