算法 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.

public class Solution {
    public boolean searchMatrix(int[][] matrix, int target) {
        
        if(matrix==null||matrix.length==0)
        {
            return false;
        }
        int len=matrix.length;
        int len2=matrix[0].length-1;
        int i=0,j=len-1;
        while(i<matrix.length&&target>matrix[i][len2])
        {
            i++;
        }
        while(j>=0&&target<matrix[j][0])
        {
            j--;
        }
        if(i!=j)
        {
            return false;
        }
        else
        {
            int[] a=matrix[j];
            int s=0,e=a.length-1;
            while(s<=e)
            {
                int mid=(s+e)/2;
                if(target==a[mid])
                {
                    return true;
                }
                else if(target<a[mid])
                {
                    e=mid-1;
                }
                else
                {
                    s=mid+1;
                }
            }
        }
        return false;
    }
}