Problem: Search a 2D Matrix

Question

Write an efficient algorithm that searches for a value in an m x n matrix. This matrix has the following properties:

Integers in each row are sorted from left to right.
The first integer of each row is greater than the last integer of the previous row.

For example,

Consider the following matrix:

[
  [1,   3,  5,  7],
  [10, 11, 16, 20],
  [23, 30, 34, 50]
]

Given target = 3, return true.

Solution

TODO

Code

public class Solution {

  public boolean searchMatrix(int[][] matrix, int target) {

    int rows = matrix.length;
    int cols = matrix[0].length;

    int begin = 0;
    int end = rows * cols - 1;

    while(begin <= end) {
      int mid = (begin + end) / 2;
      int mid_value = matrix[mid/cols][mid%cols];

      if( mid_value == target)
        return true;
      else if(mid_value < target)
        begin = mid+1;
      else
        end = mid-1;
    }

    return false;
  }
}

Performance