Problem

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.

Example

Input ::
[
  [1,   3,  5,  7],
  [10, 11, 16, 20],
  [23, 30, 34, 50]
]
Given target = 3, return true.

JavaScript Code

function searchMatrix(matrix, target) {
    if(matrix==null || matrix.length==0 || matrix[0].length==0) 
        return false;

    var m = matrix.length;
    var n = matrix[0].length;

    var start = 0;
    var end = m*n-1;

    while(start<=end){
        var mid=parseInt((start+end)/2);
        var midX=parseInt(mid/n);
        var 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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