Search a 2D Matrix II

Problem

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.

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

Code - Java

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) {
        if (matrix == null || matrix.length == 0) return 0;

        int lenX = matrix.length;
        int lenY = matrix[0].length;

        int i = lenX - 1;
        int j = 0;
        int cnt = 0;

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

        return cnt;
    }
}