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class Solution { //same as genetic mutation? public: int ladderLength(string start, string end, vector<string>& bank) { unordered_set<string> st{bank.begin(),bank.end()}; if(!st.count(end)) return 0; queue<string> q; q.push(start); int count=0; while(!q.empty()){ int s=q.size(); while(s--){ string f=q.front(); q.pop(); if(f==end) return count +1; st.erase(f); // we have visited this word ,dont visit it again //string d=f; //too many computations for(int i=0;i<f.size();i++){ char org=f[i]; for(char c='a' ; c<='z';c++){ f[i]=c; if(st.count(f)) q.push(f); } f[i]=org; //backtracking } } count++; } return 0; } };