【LeetCode】#74搜索二维矩阵(Search a 2D Matrix)

【LeetCode】#74搜索二维矩阵(Search a 2D Matrix)

题目描述

编写一个高效的算法来判断 m x n 矩阵中，是否存在一个目标值。该矩阵具有如下特性：
每行中的整数从左到右按升序排列。
每行的第一个整数大于前一行的最后一个整数。

示例

示例 1:

输入:
matrix = [
[1, 3, 5, 7],
[10, 11, 16, 20],
[23, 30, 34, 50]
]
target = 3
输出: true

示例 2:

输入:
matrix = [
[1, 3, 5, 7],
[10, 11, 16, 20],
[23, 30, 34, 50]
]
target = 13
输出: false

Description

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.

Example

Example 1:

Input:
matrix = [
[1, 3, 5, 7],
[10, 11, 16, 20],
[23, 30, 34, 50]
]
target = 3
Output: true

Example 2:

Input:
matrix = [
[1, 3, 5, 7],
[10, 11, 16, 20],
[23, 30, 34, 50]
]
target = 13
Output: false

解法

class Solution {
    public boolean searchMatrix(int[][] matrix, int target) {
        if(matrix.length==0)
            return false;
        int m = matrix.length;
        int n = matrix[0].length;
        int low = 0, high = m*n;
        while(low<high){
            int mid = (low+high)/2;
            if(matrix[mid/n][mid%n]==target){
                return true;
            }else if(matrix[mid/n][mid%n]<target){
                low = mid+1;
            }else{
                high = mid;
            }
        }
        return false;
    }
}