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.*/#include <stdio.h>#include <iostream>#include <vector>using namespace std;class Solution {public:    bool searchMatrix(vector<vector<int>>& matrix, int target) {        if(matrix.empty()) return false;int row=matrix.size(),column=matrix[0].size();if(matrix[0][0]>target || matrix[row-1][column-1]<target) return false;//寻找位于第几行int left=0,right=row-1;int mid,target_row;while(left<=right){mid=(left+right)/2;if(matrix[mid][0]==target)return true;else if(matrix[mid][0]<target)left=mid+1;elseright=mid-1;}target_row=left-1;left=0,right=column-1;while(left<=right){mid=(left+right)/2;if(matrix[target_row][mid]==target)return true;else if(matrix[target_row][mid]<target)left=mid+1;elseright=mid-1;}return false;//Runtime Error Message: reference binding to null pointer of type 'value_type' ?????//不知道什么原因??    }bool searchMatrix2(vector<vector<int>>& matrix, int target) {//把二维矩阵看成一维数组利用二分查找 val[m*column+n]=matrix[m][n]if(matrix.empty())return false;int row=matrix.size(),column=matrix[0].size();int left=0,right=row*column-1,mid;while(left<=right){mid=(left+right)/2;if(matrix[mid/column][mid%column]==target)return true;else if(matrix[mid/column][mid%column]>target)right=mid-1;elseleft=mid+1;}return false;}};int main(){Solution mys;vector<vector<int> > matrix;//={{1,2,3},{4,5,6},{7,8,9}};cout<<mys.searchMatrix(matrix,5)<<endl;return 0;}