leetcode75:search-a-2d-matrix

题目描述

请写出一个高效的在m*n矩阵中判断目标值是否存在的算法，矩阵具有如下特征：

每一行的数字都从左到右排序

每一行的第一个数字都比上一行最后一个数字大

例如：

对于下面的矩阵：

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

要搜索的目标值为3，返回true；

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, returntrue.

示例1

输入

复制

[[1,1]],0

输出

复制

false


class Solution {
public:
    /**
     * 
     * @param matrix int整型vector<vector<>> 
     * @param target int整型 
     * @return bool布尔型
     */
    bool searchMatrix(vector<vector<int> >& matrix, int target) {
        // write code here
        int rows=matrix.size();
        int cols=matrix[0].size();
        int begin=0,end=rows*cols-1;
        
        while (begin <= end)
        {
            int mid=(begin+end)/2;
            int row=mid/cols;
            int col=mid%cols;
            if (matrix[row][col] ==target)
                return true;
            else if (matrix[row][col]<target)
                begin=mid+1;
            else 
                end=mid-1;
            
        }
        return false;
    }
};