Search a 2D Matrix

Description:

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.

Code:

 bool searchMatrix(vector<vector<int>>& matrix, int target) {
        int row = matrix.size();
        if (row == 0)
            return false;
        int col = matrix[0].size();
        //每次和右上角的元素比较
        int i = 0, j = col-1;
        while ( i < row && j >= 0 )
        {
            if ( target==matrix[i][j] )
                return true;
            else if ( target < matrix[i][j] )
                j = j-1;
            else
                i = i+1;
        }
        return false;
    }