(java)leetcode74:Search a 2D Matrix

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

.

解题思路：

在二维数组中查找值，所以就是用两次二分法查找吧。先找到满足条件的行，再在该行中查找是否有那个值。

public class Solution {
public boolean searchMatrix(int[][] matrix, int target) {
if(matrix == null || matrix.length == 0 || matrix[0].length == 0)
return false;
int row = matrix.length;
int col = matrix[0].length;
int rowf = 0;
int colf = 0;
while(rowf != row)
{
if(matrix[(rowf+row)/2][0]<=target && matrix[(rowf+row)/2][col-1]>= target)
break;
else if(matrix[(rowf+row)/2][0]>target)
row = (rowf+row)/2;
else
rowf = (rowf+row)/2+1;
}
if(rowf == row)
return false;
int rerow = (rowf+row)/2;
while(colf != col)
{
if(matrix[rerow][(colf+col)/2] == target)
return true;
else if(matrix[rerow][(colf+col)/2] > target)
col = (colf+col)/2;
else
colf = (colf+col)/2+1;
}
return false;
}
}