Added NQueen Backtracking Algo in CPP

Author: softgengaurav

problems/NQueen.cpp

@@ -0,0 +1,68 @@
+#include<bits/stdc++.h>
+using namespace std;
+
+bool check(long int a, long int b, vector<pair<long int, long int> >vp)
+{
+ //cout<<"inside check"<<endl;
+ //cout<<"size of vp "<<vp.size()<<endl;
+ long int size = vp.size();
+ for(long int i=0;i<=size-1;i++)
+ {
+ //cout<<"inside loop"<<endl;
+ if(vp[i].first == a || vp[i].second == b)
+ return false;
+
+ if(abs(a-vp[i].first) == abs(b-vp[i].second))
+ return false;
+ }
+ return true;
+}
+
+bool recur_fill(long int a, long int b, vector<pair<long int, long int> >&vp, long int n)
+{
+if(b == n && a < n)
+return false;
+if(a == n)
+return true;
+bool result = check(a, b, vp);
+if(result == true)
+{
+ vp.push_back(make_pair(a, b));
+ bool val = recur_fill(a+1, 0, vp, n);
+ if(val == false)
+ {
+ pair<long int, long int>tmp = vp.back();
+ vp.pop_back();
+ return recur_fill(tmp.first, tmp.second+1, vp, n);
+ }
+}
+else
+{
+ return recur_fill(a, b+1, vp, n);
+}
+
+return true;
+}
+
+int main()
+{
+vector<pair<long int, long int> >vp;
+vp.clear();
+long int n;
+cin>>n;
+recur_fill(0, 0, vp, n);
+for(long int i=0;i<=vp.size()-1;i++)
+{
+ long int c = vp[i].second;
+ for(long int j=0;j<c;j++)
+ {
+ cout<<" * ";
+ }
+ cout<<" Q ";
+ for(long int j=c+1;j<n;j++)
+ {
+ cout<<" * ";
+ }
+ cout<<endl;
+}
+}