p240

发表于 | 分类于 |

LeetCode p240 Search a 2D Matrix II 题解

1.题目：

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 in ascending from left to right.
Integers in each column are sorted in ascending from top to bottom.

For example,

Consider the following matrix:

[
[1, 4, 7, 11, 15],
[2, 5, 8, 12, 19],
[3, 6, 9, 16, 22],
[10, 13, 14, 17, 24],
[18, 21, 23, 26, 30]
]

Given target = 5, return true.
Given target = 20, return false.

题意：

输入一个二位数组，一个目标数，查找数组中是否含有这个数。

2.解题思路:

二分查找，并减去部分分支。

3.代码

[title] [] [url] [link text]
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
 
public class Solution {
    public boolean searchMatrix(int[][] matrix, int target) {
        int n = matrix.length;
		for (int i = 0; i < n; i++) {
			if (matrix[i][0] > target)
				break;
			int left = 0;

			int mid;
			int m = matrix[i].length;
			int right = m - 1;
			for (;;) {
				mid = (left + right) / 2;
				if (left > right)
					break;
				if (matrix[i][mid] == target)
					return true;

				if (left == right)
					break;
				if (matrix[i][mid] > target)
					right = mid;
				if (matrix[i][mid] < target)
					left = mid + 1;
			}
		}
		return false;
    }
}

4.一些总结：