find number of element less than equal to number in the matrix using two pointer code example

Example: two pointer approach java

The algorithm basically uses the fact that the input array is 
sorted. We start the sum of extreme values (smallest and 
largest) and conditionally move both pointers. We move left 
pointer i when the sum of A[i] and A[j] is less than X. We 
do not miss any pair because the sum is already smaller than X. 
Same logic applies for right pointer j.