How do I search for a number in a 2d array sorted left to right and top to bottom?

Question

I was recently given this interview question and I\'m curious what a good solution to it would be.

Say I\'m given a 2d array where all the numbers i

Answer 1

If O(M log(N)) solution is ok for an MxN array -

template 
struct MN * get(int a[][n], int k, int M, int N){
  struct MN *result = new MN;
  result->m = -1;
  result->n = -1;

  /* Do a binary search on each row since rows (and columns too) are sorted. */
  for(int i = 0; i < M; i++){
    int lo = 0; int hi = N - 1;
    while(lo <= hi){
      int mid = lo + (hi-lo)/2;
      if(k < a[i][mid]) hi = mid - 1;
      else if (k > a[i][mid]) lo = mid + 1;
      else{
        result->m = i;
        result->n = mid;
        return result;
      }
    }
  }
  return result;
}

Working C++ demo.

Please do let me know if this wouldn't work or if there is a bug it it.