Check out example codes for "two sum problem in c++". It will help you in understanding the concepts better.

Code Example 1

bool twosum(int A[], int N, int X) {
  	sort(A, A+N);
    int i = 0, j = N-1;
    while (i < j) {
        if (A[i] + A[j] == X) return true;
        else if (A[i] + A[j] > X) j--;
        else i++;
    }
    return false;
}

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