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

.

原题链接：https://oj.leetcode.com/problems/search-a-2d-matrix/

题目：在m * n 的矩阵中查找目标值是否存在。

比較好的办法就是二分查找。即将矩阵总体看成一个数组来处理。

public boolean searchMatrix(int[][] matrix, int target) {
if(matrix == null || matrix.length == 0 || matrix[0].length == 0)
return false;
int m = matrix.length;
int n = matrix[0].length;
int start = 0;
int end = m * n - 1;
while (start <= end) {
int mid = (start + end) / 2;
int x = mid / n;
int y = mid % n;
if (matrix[x][y] == target)
return true;
if (matrix[x][y] < target)
start = mid + 1;
else
end = mid - 1;
}
return false;
}