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.

public class Solution {
    public boolean searchMatrix(int[][] matrix, int target) {
        if (matrix.length == 0 || matrix[0].length == 0) {
            return false;
        }
        int m = matrix.length;
        int n = matrix[0].length;
        int start = 0;
        int end = m * n - 1;
        while (start <= end) {
            int mid = (start + end) / 2;
            int midVal = matrix[mid / n][mid % n];
            if (midVal == target) {
                return true;
            } else if (midVal > target) {
                end = mid - 1;
            } else {
                start = mid + 1;
            }
        }
        return false;
    }
}

Note: O(log(m*n))

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