LeetCode 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.

 

搜索矩阵中是否存在相应元素。

由于限制条件，这个矩阵的行元素是递增的，因此实际就是一个二分查找的过程。

 

代码：

class Solution {public:    bool searchMatrix(vector<vector<int> > &matrix, int target) {        int m=matrix.size(),n;if(m==0)return false;elsen=matrix[0].size();int first=0,last=m*n-1,mid;//头，尾，中while(first<=last)//二分查找{mid=(first+last)/2;if(matrix[mid/n][mid%n]==target)return true;else if(matrix[mid/n][mid%n]>target)last=mid-1;elsefirst=mid+1;}return false;    }};