Lintcode: Search a 2D matrix II

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

很巧妙的思路，可以从左下或者右上开始找

 1 public class Solution {

 2     /**

 3      * @param matrix: A list of lists of integers

 4      * @param: A number you want to search in the matrix

 5      * @return: An integer indicate the occurrence of target in the given matrix

 6      */

 7     public int searchMatrix(int[][] matrix, int target) {

 8         // write your code here

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

10         int m = matrix.length;

11         int n = matrix[0].length;

12         int count = 0;

13         int row = m-1;

14         int col = 0;

15         while (row>=0 && row<m && col>=0 && col<n) {

16             int cur = matrix[row][col];

17             if (cur == target) {

18                 count++;

19                 col++;

20                 row--;

21             }

22             else if (cur > target) {

23                 row--;

24             }

25             else col++;

26         }

27         return count;

28     }

29 }