[leetcode] sword finger offer 04 Search in two-dimensional array

subject ：

 The finger of the sword  Offer 04.  Search in a two-dimensional array 
 In a  n * m  In a two-dimensional array , Each row is sorted in ascending order from left to right , Each column is sorted in ascending order from top to bottom . Please complete an efficient function , Enter such a two-dimensional array and an integer , Determine whether the array contains the integer .

 Example :
 The existing matrix  matrix  as follows ：

[
  [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.
 Limit ：
0 <= n <= 1000
0 <= m <= 1000

Linear search :
Start at the top right .

class Solution {
    
    public boolean findNumberIn2DArray(int[][] matrix, int target) {
    
        if(matrix == null || matrix.length == 0) return false;
        int n = matrix.length - 1;
        int m = matrix[0].length - 1;
        for(int i = 0,j = m ; i <= n && j >= 0;){
    
            if(target < matrix[i][j]) j--;
            else if (target > matrix[i][j]) i++;
            else {
    
                return true;
            }
        }           
        return false;
    }
}

Time complexity ：O(m+n)
Spatial complexity ：O(1)