[leetcode] 【查找】 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

.

题意

判断一个矩阵中是否包含目标元素，矩阵有两个特性：从左到右排序；每一行第一个元素比上一行最后一个元素大。

题解

使用二分法，把矩阵看成是一维数据处理。   长度为col*raw          用的时候下标为    mid/row   mid%row  

class Solution {
public:
bool searchMatrix(vector<vector<int>>& matrix, int target) {
if(matrix.empty()) return false;
const size_t high=matrix.size();
const size_t len=matrix[0].size();
int begin=0,end=high*len-1,mid=0;
while(begin<end)
{
mid=(begin+end)/2;
int val=matrix[mid/len][mid%len];
if(val==target) return true;
if(val>target) end=mid;
else begin=mid+1;
}
if(matrix[begin/len][begin%len]==target ) return true;
return false;
}
};