Search a 2D Matrix

问题：二维数组中是否存在一个数

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class Solution { public:     bool dfs(vector<vector<int> > &matrix,int target,int n)     {         if(n==matrix.size()) return false;         if(matrix[n][0]>target) return false;         for(int i=0;i<matrix[n].size();i++)         {             if(matrix[n][i]==target) return true;             if(matrix[n][i]>target) return false;         }         return dfs(matrix,target,n+1);     }     bool searchMatrix(vector<vector<int> > &matrix, int target) {         return dfs(matrix,target,0);     } };