LeetCode 127 Word Ladder

struct Node
{
    string word;
    int dis;
    Node(){}
    Node(string word,int dis)
    {
        this->word = word;
        this->dis = dis;
    }
};
class Solution {
    
public:
 
    int vis[100005];
    queue<Node> q;
    int ladderLength(string beginWord, string endWord, vector<string>& wordList) {
        
        q.push(Node(beginWord,1));
        int l = wordList.size();
        int tag=0;
        memset(vis,0,sizeof(vis));
        for(int i=0;i<l;i++)
        {
            if(endWord==wordList[i])
            {
                tag=1;
            }
        }
        if(tag==0)
            return 0;
       int ans = 0;
        while(!q.empty())
        {
            Node term = q.front();
            q.pop();
            if(term.word == endWord)
            {
                ans = term.dis;
                break;
            }
            for(int i=0;i<l;i++)
            {
                if(change(term.word,wordList[i]))
                {
                    if(vis[i]==0)
                    {
                        vis[i]=1;
                        q.push(Node(wordList[i],term.dis+1));
          
                    }
                }
            }
        }
        return ans;

    }
    
     bool change(string a ,string b)
    {
        int num = 0;
        int l = a.length();
        for(int i=0;i<l;i++)
        {
            if(a[i]!=b[i])
                num++;
        }
        if(num==1)
            return true;
        else
            return false;
    }
};