无法解决C++中的内存读取和分段错误

Question

我正在为leetcode编写一个解决方案程序。我遇到了无法解决的内存读取错误和分段错误。我试着修改代码，试图删除错误
例如：在numIslands函数的最后几行中，我尝试将coordinates声明为数组而不是指针，但结果没有改变
*(last + 1) = *(coordinates + 1);在numIslands函数中似乎根本不起作用。我对下一步该做什么一无所知。

#include <iostream>
#include <string>
#include <vector>
#include <map>
namespace p200 {
using std::cout;
using std::cin;
using std::endl;
using std::string;
using std::vector;
using std::map;
}
class Solution {
private:
int count_islands = 0;

public:
int *last;
int numIslands(vector<vector<char>>& grid) {
if (grid.size() == 0) return count_islands;
if (grid.size() == 1 && grid[0].size() == 1) return grid[0][0] - 48;
vector<vector<int>> grid_copy;
vector<int> in;
for (size_t index = 0; index < grid.size(); ++index) {
for (size_t index0 = 0; index0 < grid[index].size(); ++index0) {
(grid[index][index0] == '0')
? in.push_back(0)
: in.push_back(INT_MAX);
}
grid_copy.push_back(in);
in.clear();
}
int * coordinates = new int[2];
*coordinates = 0;
*(coordinates + 1) = 0;
last = new int[2];
*last = *coordinates;
*(last + 1) = *(coordinates + 1);
find_island(grid_copy, coordinates);
return count_islands;
}
void find_island(vector<vector<int>> & arg_grid, int* arg_coordinates) {
if (arg_grid[*arg_coordinates][*(arg_coordinates + 1)] == INT_MAX) {
*last = *arg_coordinates;
*(last + 1) = *(arg_coordinates + 1);
map_island(arg_grid, arg_coordinates, 1);
} else {
if (*(arg_coordinates + 1) < arg_grid[*arg_coordinates].size()) {
*(arg_coordinates + 1) = *(arg_coordinates + 1) + 1;
find_island(arg_grid, arg_coordinates);
}
if (*(arg_coordinates + 1) == arg_grid[*arg_coordinates].size()) {
if (*arg_coordinates == arg_grid.size()) return;
*arg_coordinates = *arg_coordinates + 1;
*(arg_coordinates + 1) = 0;
find_island(arg_grid, arg_coordinates);
}
}   
}
void map_island(vector<vector<int>> & arg_grid, int* arg_coordinates, int arg_new) {
arg_grid[*arg_coordinates][*(arg_coordinates + 1)] = count_islands + (arg_new * 1);
if (arg_new) count_islands = count_islands + 1;
if (*arg_coordinates != 0 && *arg_coordinates - 1 == INT_MAX) {
*arg_coordinates = *arg_coordinates - 1;
map_island(arg_grid, arg_coordinates, 0);
*arg_coordinates = *arg_coordinates + 1;
}
if ((*arg_coordinates < arg_grid.size() - 1)
&& *arg_coordinates + 1 == INT_MAX) {
*arg_coordinates = *arg_coordinates + 1;
map_island(arg_grid, arg_coordinates, 0);
*arg_coordinates = *arg_coordinates - 1;
}
if (*(arg_coordinates + 1) != 0 && *(arg_coordinates + 1) - 1 == INT_MAX) {
*(arg_coordinates + 1) = *(arg_coordinates + 1) - 1;
map_island(arg_grid, arg_coordinates, 0);
*(arg_coordinates + 1) = *(arg_coordinates + 1) + 1;
}
if (*(arg_coordinates + 1) < arg_grid[*arg_coordinates].size() - 1
&& *(arg_coordinates + 1) + 1 == INT_MAX) {
*(arg_coordinates + 1) = *(arg_coordinates + 1) + 1;
map_island(arg_grid, arg_coordinates, 0);
*(arg_coordinates + 1) = *(arg_coordinates + 1) - 1;
}
find_island(arg_grid, last);
}
};

int main() {
vector<vector<char>> input;
input.push_back(vector<char>({'1','1','1','1','0'}));
input.push_back(vector<char>({'1','1','0','1','0'}));
input.push_back(vector<char>({'1','1','0','0','0'}));
input.push_back(vector<char>({'0','0','0','0','0'}));
Solution solver;
cout << "Number of Island: " << solver.numIslands(input) << endl;
return 0;
}

Answer 1

我已经通过gdb运行了它。经过一番挖掘，错误是：

void find_island(vector<vector<int>> & arg_grid, int* arg_coordinates) {
if (arg_grid[*arg_coordinates][*(arg_coordinates + 1)] == INT_MAX) {
*last = *arg_coordinates;
*(last + 1) = *(arg_coordinates + 1);
map_island(arg_grid, arg_coordinates, 1);
} else {
if (*(arg_coordinates + 1) < arg_grid[*arg_coordinates].size()) {
*(arg_coordinates + 1) = *(arg_coordinates + 1) + 1;
find_island(arg_grid, arg_coordinates);
}
if (*(arg_coordinates + 1) == arg_grid[*arg_coordinates].size()) {
if (*arg_coordinates == arg_grid.size()) return;
*arg_coordinates = *arg_coordinates + 1;
*(arg_coordinates + 1) = 0;
find_island(arg_grid, arg_coordinates);
}
}
}

在第二个if中，进行边界检查，然后递增。您应该首先递增，然后进行边界检查，如下所示：

*arg_coordinates = *arg_coordinates + 1;
if (*arg_coordinates == arg_grid.size()) return;

另外，请使用vector.at()而不是operator[]。它生成更可读、更易于解释的调试消息。正如其他人指出的那样，*(arg_coordinates + 1) = arg_coordinates[1]将使代码可读性更强。

对于其他类似的问题，我建议使用调试器。

编辑：我运行了代码，意识到其中还有其他一些错误。其中一个岛屿被计数了两次，所以它给出了错误的结果，但从技术上讲，这不是问题所在。