Search a 2D Matrix II
30% Accepted
Write an efficient algorithm that searches for a value in an m x n matrix,
return the occurrence of it.
This matrix has the following properties:
* Integers in each row are sorted from left to right.
* Integers in each column are sorted from up to bottom.
* No duplicate integers in each row or column.
Have you met this question in a real interview? Yes
Example
Consider the following matrix:
[
[1, 3, 5, 7],
[2, 4, 7, 8],
[3, 5, 9, 10]
]
Given target = 3, return 2.
Challenge
- O(m+n) time and O(1) extra space
Tags Expand
- Matrix
思路
- 非常精妙的解法
- 根据其特殊的性质,不再使用二分
public class Solution {
/**
* @param matrix: A list of lists of integers
* @param: A number you want to search in the matrix
* @return: An integer indicate the occurrence of target in the given matrix
*/
public int searchMatrix(int[][] matrix, int target) {
// check corner case
if (matrix == null || matrix.length == 0) {
return 0;
}
if (matrix[0] == null || matrix[0].length == 0) {
return 0;
}
// from bottom left to top right
int n = matrix.length;
int m = matrix[0].length;
int x = n - 1;
int y = 0;
int count = 0;
while (x >= 0 && y < m) {
if (matrix[x][y] < target) {
y++;
} else if (matrix[x][y] > target) {
x--;
} else {
count++;
x--;
y++;
}
}
return count;
}
}