LeetCode_74 Search a 2D Matrix

题目：

---

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.

分析：

class Solution {
    public boolean searchMatrix(int[][] matrix, int target) {
        //给定一个二维矩阵，其特征为：每行数据递增排序，每一行的第一个数据大于上一行的最后一个数据
        //思路：从最下面一排的第一个开始选择比较,依次往上走
        
        if(matrix==null||matrix.length==0||matrix[0].length==0){
            return false;
        }
        int i=matrix.length-1;
        int j=0;
        while(i>=0&&j<=matrix[0].length-1){
            if(matrix[i][j]==target){
                return true;
            }else if(matrix[i][j]>target){
                i--;
            }else{
                j++;
            }
        }
        return false;
    }
}