[leedcode 74] Search a 2D Matrix

Write an efficient algorithm that searches for a value in an m x n matrix. This matrix has the following properties:

 

• Integers in each row are sorted from left to right.
• The first integer of each row is greater than the last integer of the previous row.

 

For example,

Consider the following matrix:

[
  [1,   3,  5,  7],
  [10, 11, 16, 20],
  [23, 30, 34, 50]
]

Given target = 3, return true.

public class Solution {
    public boolean searchMatrix(int[][] matrix, int target) {
        //从右上开始遍历
        //注意循环的写法，不是两层循环！！时间复杂度是O（m+n）？
        int row=matrix.length;
        int col=matrix[0].length;
        int i=0;
        int j=col-1;
        while(i<row&&j>=0){
            if(matrix[i][j]==target) return true;
            if(matrix[i][j]>target){
                j--;
            }else i++;
        }
        return false;
    }
}