74. Search a 2D Matrix

class Solution {
    public boolean searchMatrix(int[][] matrix, int target) {
        if (matrix == null || matrix.length == 0) return false;
        int m = matrix.length, n = matrix[0].length;
        int lo = 0, hi = m * n - 1;
        while (lo <= hi) {
            int mid = lo + (hi - lo) / 2;

            if (matrix[mid / n][mid % n] == target) {
                return true;
            }

            if (matrix[mid / n][mid % n] < target) {
                lo = mid + 1;
            } else {
                hi = mid - 1;
            }
        }

        return false;
    }
}