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.

有序数组采用二分搜索，矩阵可以采用两次二分

第一次，对row进行二分，按照每行最大数二分，找到所在行

第二次，对col进行二分

public class Solution {
    public boolean searchMatrix(int[][] matrix, int target) {
        int row=matrix.length;
        int col=matrix[0].length;
        int middle = 0;
		int start = 0;
		int end = row-1;
		while (start<end) {
			middle = (start + end) / 2;
			if (matrix[middle][col-1] == target)
				return true;
			if(matrix[middle][col-1] < target)
				start=middle+1;
			else
				end=middle;
		}
		row=start;  //确定所在行
		start=0;
		end=col;
		while(start<end){
			middle=(start + end) / 2;
			if (matrix[row][middle] == target)
				return true;
			if(matrix[row][middle] < target)
				start=middle+1;
			else
				end=middle;
		}
		return false;
    }
}