leetcode240. Search a 2D Matrix II

240. Search a 2D Matrix II

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 in ascending from left to right.

Integers in each column are sorted in ascending from top to bottom.

For example,

Consider the following matrix:

[
[1,   4,  7, 11, 15],
[2,   5,  8, 12, 19],
[3,   6,  9, 16, 22],
[10, 13, 14, 17, 24],
[18, 21, 23, 26, 30]
]
Given target = 5, return true.

Given target = 20, return false.

解法

从左下角开始，如果比target小，则向右走；如果比target大，则向上走；直到走到右上的位置。

public class Solution {
public boolean searchMatrix(int[][] matrix, int target) {
if (matrix.length == 0 || matrix == null) {
return false;
}
if (matrix[0].length == 0 || matrix[0] == null) {
return false;
}

int row = matrix.length;
int column = matrix[0].length;
int i = row - 1;
int j = 0;

while (j < column && i >= 0) {
if (matrix[i][j] == target) {
return true;
} else if (matrix[i][j] < target) {
j++;
} else {
i--;
}
}

return false;
}
}