Search a 2D Matrix II(lintcode 38)

Description

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.

Interface

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) {
        // write your code here
    }
}

Solution

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) {
        // write your code here
        if (matrix == null || matrix.length == 0) {
            return 0;
        }

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

        int m = matrix.length;
        int n = matrix[0].length;
        int a = m - 1;
        int b = 0;
        int count = 0;

        while (a >= 0 && b < n) {
            if (matrix[a][b] == target) {
                --a;
                ++b;
                ++count;
            } else if (matrix[a][b] > target) {
                --a;
            } else {
                ++b;
            }
        }

        return count;
    }
}