[Leetcode] Search a 2D Matrix

Problem

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.

Algorithm

Search the matrix from row L to row R.  Compare the target with the first, last and middle element in the middle row M = (L+R)/2. 

If target < matrix[M][0], search row L to row M-1

else if target > matrix[M][end], search row M+1 to row R

else, binary search in row M. 

Code