【LeetCode题目记录-13】二分搜索排序后的二维数组

Search a 2D Matrix

Writean 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

.

【分析-原创】

/**
* 创建时间：2014年9月24日 上午11:26:06 项目名称：Test
*
* @author Cao Yanfeng
* @since JDK 1.6.0_21 类说明： 查找排序后的二维矩阵是否存在一个数 应用两层的二分查找，第一层是查找行
*/
public class FindMatrixTest {

/**
* @param args
*/
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 } };
System.out.println(searchMatrix(matrix, 13));

}

public static boolean searchMatrix(int[][] matrix, int target) {
int m = matrix.length;
int n = matrix[0].length;
int i = 0, j = m - 1;
while (i <= j) {
int middleRow = i + ((j - i) >> 1);
if (target < matrix[middleRow][0]) {
j = middleRow - 1;
continue;
} else if (target > matrix[middleRow][n - 1]) {
i = middleRow + 1;
continue;
} else if (target >= matrix[middleRow][0]
&& target <= matrix[middleRow][n - 1]) {
return find(matrix[middleRow], 0, n - 1, target);
}
}
return false;
}

public static boolean find(int[] matrixRow, int start, int end, int target) {
while (start <= end) {
int middle = start + ((end - start) >> 1);
if (matrixRow[middle] == target) {
return true;
} else if (matrixRow[middle] > target) {
end = middle - 1;
} else if (matrixRow[middle] < target) {
start = middle + 1;
}

}
return false;
}
}