[Leetcode] Search a 2D Matrix

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.

    bool searchMatrix(vector<vector<int> > &matrix, int target) {
        int b = 0;
        int e = matrix.size() * matrix[0].size() - 1;
        while(b <= e)
        {
            //treat the whole matrix as a long array and do the binary search
            int m = (b+e)/2;
            int row = m / matrix[0].size();
            int col = m % matrix[0].size();
            if (matrix[row][col] == target)
                return true;
            else if (target < matrix[row][col])
                e = m - 1;
            else
                b = m + 1;
        }
        
        return false;
    }