Trie实现编译但在输入数据时崩溃

Question

我正在使用topcoder.com的trie实现并尝试将单词存储在trie结构中。我用网上的代码。我似乎无法找出我输入失败的原因。

    #include<iostream>
#include<queue>
#include<vector>
#include<algorithm>
#include<map>
#include<string>
using namespace std;
#define M 10000
#define tr(c,i) for(typeof(c.begin()) i=c.begin(); i!=c.end(); ++i)

class Trie {
    public:
        int words;
        int prefixes;
        Trie* edges[26];
        Trie();
        void addWord(string word);
        int countWords(string word);
        int countPrefixes(string prefix);
};

Trie::Trie() {
    words = 0;
    prefixes = 0;
    for(int i=0;i<26;++i)
        edges[i] = NULL;
}

void Trie::addWord(string word) {
    if (word.size()==0) 
        words = words+1;
    else {
        prefixes = prefixes+1;
        char k = word[0];
        if (edges[k-'A']==NULL) {
            edges[k-'A'] = new Trie;
        }
        edges[k-'A']->addWord(word.substr(1));
    }
}

int Trie::countWords(string word) {
    if (word.size()==0)
        return words;
    else {
        char k = word[0];
        if (edges[k-'A']==NULL)
            return 0;
        else {
            return edges[k-'A']->countWords(word.substr(1));
        }
    }
}

int Trie::countPrefixes(string prefix) {
    if (prefix.size()==0)
        return prefixes;
    else {
        char k = prefix[0];
        if (edges[k-'A']==NULL)
            return 0;
        else {
            return edges[k-'A']->countPrefixes(prefix.substr(1));
        }
    }
}

int main() 
{
    int tests;
    cin>>tests;
    for(int t=1;t<=tests;t++)
    {
        Trie root;
        int n;
        cin>>n;
        string str[n];
        int ans=0;
        for(int i=0;i<n;i++)
        {
            cin>>str[i];
            root.addWord(str[i]);
        }
        for(int i=0;i<n;i++)
        {
            ans+=root.countPrefixes(str[i]);
        }
        cout<<ans;
    }
    return 0;
}

有什么可能出错的建议吗？谢谢！