我的代码可以编译，执行，但某些输入会崩溃

Question

我试图获得两个字符串的最长公共子序列的长度。 它适用于大多数输入，但对于指定的输入会崩溃。 代码如下：

#include <cmath>
#include <string>

#include <vector>
#include <iostream>
#include <algorithm>
using namespace std;

/* Utility function to get max of 2 integers */
int max(int a, int b)
{
    return (a > b)? a : b;
}

/* Returns length of LCS for X[0..m-1], Y[0..n-1] */
int lcs(string &X, string &Y, int m, int n )
{
    int L[5000 + 1][5000 + 1] = {0};
    int i, j;

    /* Following steps build L[m+1][n+1] in bottom up fashion. Note 
      that L[i][j] contains length of LCS of X[0..i-1] and Y[0..j-1] */
    for (i = 0; i <= m; i++)
    {
        for (j = 0; j <= n; j++)
        {
            if (i == 0 || j == 0)
                L[i][j] = 0;

            else if (X.at(i - 1) == Y.at(j - 1))
                L[i][j] = L[i - 1][j - 1] + 1;

            else
                L[i][j] = max(L[i - 1][j], L[i][j - 1]);
        }
    }

    /* L[m][n] contains length of LCS for X[0..n-1] and Y[0..m-1] */
    return L[m][n];
}

int main() {
    string A, B;
    cin >> A;
    cin >> B;

    int count1 = lcs(A, B, A.size(), B.size());

    cout << count1;
    return 0;
}

输入的字符串如下：

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

我尝试使用C样式的字符串，但是它崩溃了。 如果输入字符串大于阈值，我也尝试将其分为多个字符串，但仍然无法正常工作。 希望有人发现错误。 提前致谢。

Answer 1

此本地声明：

    int L[5000 + 1][5000 + 1] = {0};

在调用堆栈上分配了2500万个int -s，即4个字节的字（即100兆字节）。 在当前的台式机和笔记本电脑上，典型的调用堆栈最多只有几兆字节，因此最好在每个调用帧中使用几千字节（但YMMV）。

您一定会遇到堆栈溢出的情况 。

您可能会考虑使用堆分配的C ++ 标准容器 ，例如std::vector （即使在堆栈上具有本地容器变量时，大多数实际数据也是堆分配的）。

正如我所评论的，该学习更多调试工具了： g++ -Wall -Wextra -g ，也许还有-fsanitize=address ， gdb调试器， valgrind ，strace。 详细信息是特定于实现的。

当然，请阅读几本有关C ++ 11（或C ++ 14）的好书： C ++与编程 之旅 -使用C ++的原理与实践

如果您在Linux上进行编码，那么高级Linux编程也值得一读。