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 in ascending from left to right.
• Integers in each column are sorted in ascending from top to bottom.

Example:

Consider the following matrix:

[  

    [1,   4,  7, 11, 15],  

    [2,   5,  8, 12, 19],  

    [3,   6,  9, 16, 22],  

    [10, 13, 14, 17, 24],  

    [18, 21, 23, 26, 30]

]

Given target = 5, return true.

Given target = 20, return false.