【leetcode】74. Search 2D matrix

subject ：
74. Search for a two-dimensional matrix
Write an efficient algorithm to judge m x n Matrix , Is there a target value . The matrix has the following characteristics ：

The integers in each row are arranged in ascending order from left to right .
The first integer in each row is greater than the last integer in the previous row .

Example 1：

Input ：matrix = [[1,3,5,7],[10,11,16,20],[23,30,34,60]], target = 3
Output ：true
Example 2：

Input ：matrix = [[1,3,5,7],[10,11,16,20],[23,30,34,60]], target = 13
Output ：false

Tips ：
m == matrix.length
n == matrix[i].length
1 <= m, n <= 100
-104 <= matrix[i][j], target <= 104

Ideas ：
Start at the top right .
Time complexity ：O(log n)

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