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;

    }