Leetcode N-queens/n-queens II, backtracking, C + +

Thanks to the video of Stanford cs106b lecture ten by Julie Zelenski for the nice explanation of recursion and backtracking , highly recommended.

N-queens (12ms)

classSolution { vector<vector<string>>AnsintN//int Numofsol;    voidAddto_ans (string&conf) { vector<string>vecstrtmp;stringStrtmp (N,'. '); for(Autoind:conf) {vecstrtmp.push_back (strtmp); Vecstrtmp.back () [(size_t) ind-1]=' Q '; } ans.push_back ( vector<string>());    Ans.back (). Swap (VECSTRTMP); }voidReclistnqueens (stringSofar,stringRest) {if(Rest.empty ()) {//++numofsol;Addto_ans (SOFAR); }Else{intI,j,len=sofar.size (), flag; for(i=0; I<rest.size (); ++i) { for(j=0; j<len;++j) {flag=1;if(Sofar[j]-rest[i]==len-j | | sofar[j]-rest[i]==j-len) {flag=0; Break; }                }if(flag) Reclistnqueens (Sofar+rest[i],rest.substr (0, i) +rest.substr (i+1)); }        }    } Public: vector<vector<string>>Solvenqueens (intN) {ans.clear ();//numofsol=0;N=n;stringStr for(intI=1; i<=n;++i) Str.push_back (i); Reclistnqueens ("", str);returnAns }};

With a tiny modification,
N-queens II (8ms)

Class Solution {//vector<vector<string>> ans;    intNintNumofsol;/*void Addto_ans (string &conf) {vector<string> vecstrtmp;        String strtmp (N, '. ');            for (auto ind:conf) {vecstrtmp.push_back (strtmp);        Vecstrtmp.back () [(size_t) ind-1]= ' Q ';        } ans.push_back (Vector<string> ());    Ans.back (). Swap (VECSTRTMP); }*/    voidReclistnqueens (stringSofar,stringRest) {if(Rest.empty ()) {++numofsol;//addto_ans (SOFAR);}Else{intI,j,len=sofar.size (), flag; for(i=0; I<rest.size (); ++i) { for(j=0; j<len;++j) {flag=1;if(Sofar[j]-rest[i]==len-j | | sofar[j]-rest[i]==j-len) {flag=0; Break; }                }if(flag) Reclistnqueens (Sofar+rest[i],rest.substr (0, i) +rest.substr (i+1)); }        }    } Public:int Totalnqueens(intN) {//ans.clear ();Numofsol=0; N=n;stringStr for(intI=1; i<=n;++i) Str.push_back (i); Reclistnqueens ("", str);returnNumofsol; }};

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Leetcode N-queens/n-queens II, backtracking, C + +