LeetCode - Search a 2D Matrix

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 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

.

思路：

二分查找

package array;

public class SearchA2DMatrix {

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

return false;
}

public static void main(String[] args) {
// TODO Auto-generated method stub
int[][] matrix = {
{ 1, 3, 5, 7 },
{ 10, 11, 16, 20 },
{ 23, 30, 34, 50}
};
SearchA2DMatrix s = new SearchA2DMatrix();
System.out.println(s.searchMatrix(matrix, 8));
}

}