行933:字符34:运行时错误:引用绑定到类型为'struct value_type'(stl_vector.h)的空指针-Leet Code Spiral

问题描述

我试图解决Leetcode问题54-螺旋并卡在空向量输入中.

I tried to solve Leetcode Problem 54 - spiraland got stuck in empty vector input.

问题在于螺旋清单.输入为2d向量，输出应为螺旋方向写入的向量列表.

the question is about spiral list. input is 2d vector and output should be vector list which written by spiral direction.

Input:
[
  [1, 2, 3, 4],
  [5, 6, 7, 8],
  [9,10,11,12]
]
Output: [1,2,3,4,8,12,11,10,9,5,6,7]

问题是输入为空列表时.

problem is when input is empty list.

Input: []

它产生运行时错误.

通过了另一个测试用例，除了 [] 之类的空输入.

another testcases passed except empty input like [] .

在我的Mac OSX终端中进行测试时似乎没有运行时错误，但是Leetcode说

It seems no runtime error during testing in my mac OSX terminal,but Leetcode says

'行933:字符34:运行时错误:引用绑定到类型为'struct value_type'(stl_vector.h)的空指针 '

'Line 933: Char 34: runtime error: reference binding to null pointer of type 'struct value_type' (stl_vector.h) '

这里是链接 https://leetcode.com/problems/spiral-matrix/

Here is linkhttps://leetcode.com/problems/spiral-matrix/

我还在下面附加代码...

Also I attach codes below ...

class Solution {
public:

vector<int> answer;
int left = 0, right = 0;
vector<int> spiralOrder(vector<vector<int>>& matrix) {
    if(matrix[0].size()<1) return {};
    vector<vector<int>> flag(matrix.size(),vector<int>(matrix[0].size(),0));
        while(1){
           flag[left][right] =1;
           answer.push_back(matrix[left][right]);

           if(right+1<matrix[0].size() && flag[left][right+1] == 0){
               ++right;
               continue;
           }
           else if(left+1<matrix.size() && flag[left+1][right] == 0 ){
               ++left;
               continue;
           }
           else if(right-1>=0 && flag[left][right-1]==0){
               --right;
               continue;
           }
           else if(left-1>=0  && flag[left-1][right]==0){
               --left;
               continue;
           }
           else break;
        }
    return answer;
}
};

推荐答案

感谢您的评论，我想出了自己解决这个问题的方法.我改变了

Thanks for comments, I figure out how to solve this one myself.I changed

if(matrix[0].size()<1

到

if(matrix.empty()) return {};

成功了.我也发现我的算法是错误的，并将其修复.

and it worked.Also I found my algorithm was wrong and fixed it.

    using namespace std;

    enum class Direction{
          RIGHT,
          DOWN,
          LEFT,
          UP
        };
    class Solution {
    public:
        Direction direc;
        vector<int> answer;
        int left = 0, right = 0;
        vector<int> spiralOrder(vector<vector<int>>& matrix) {
          Direction direc = Direction::RIGHT;
          if(matrix.empty()) return {};
        vector<vector<int>> flag(matrix.size(),vector<int>(matrix[0].size(),0));

            while(1){
              flag[left][right] =1;
              answer.push_back(matrix[left][right]);
              switch(direc){
              case Direction::RIGHT:
               if(right+1<matrix[0].size() && flag[left][right+1] == 0){
                   ++right;
                   continue;
               }
               else if(left+1<matrix.size() && flag[left+1][right] == 0 ){
                   ++left;
                   direc = Direction::DOWN;
                   continue;
               }
               else break;
             case Direction::DOWN:
              if(left+1<matrix.size() && flag[left+1][right] == 0 ){
                   ++left;
                   continue;
                }
              else if(right-1>=0 && flag[left][right-1]==0){
                   --right;
                   direc = Direction::LEFT;
                   continue;
               }
               else break;
              case Direction::LEFT:
               if(right-1>=0 && flag[left][right-1]==0){
                   --right;
                   continue;
               }
               else if(left-1>=0  && flag[left-1][right]==0){
                   --left;
                   direc = Direction::UP;
                   continue;
              }
               else break;
              case Direction::UP:
               if(left-1>=0  && flag[left-1][right]==0){
                   --left;
                   continue;
              }
               else if(right+1<matrix[0].size() && flag[left][right+1] == 0){
                   ++right;
                   direc = Direction::RIGHT;
                   continue;
               }
               else break;
            }
            break;
          } // switch-case
        return answer;
    }
};

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