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

.

Solution 1. Binary Search
// The matrix is divided into 3 parts: smaller, bigger and unknown.
public class Solution {
public boolean searchMatrix(int[][] matrix, int target) {
int m = matrix.length;
int n = matrix[0].length;
int i = 0, j = n-1;
while (i<m && j>=0) {
if (target == matrix[i][j]) return true;
if (matrix[i][j] > target) {
j--;
}else if (matrix[i][j] < target) {
i++;
}
}

return false;
}
}