LeetCode - Search a 2D Matrix (Java)

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

1) Integers in each row are sorted from left to right. 2) The first integer of each row is greater than the last integer of the previous row.

public class Solution {
    public boolean searchMatrix(int[][] matrix, int target) {
        if(matrix==null || 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 midX=mid/n;
            int midY=mid%n;
 
            if(matrix[midX][midY]==target) 
                return true;
 
            if(matrix[midX][midY]<target){
                start=mid+1;
            }else{
                end=mid-1;
            }
        }
 
        return false;
    }
}

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