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Commit 4e580b2

sauravjaiswalsj sauravjaiswalsj

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Merge pull request fnplus#656 from akshitagupta15june/master

Create N-queen-problem.cpp

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Data Structures/Backtracking
- N-queen-problem.cpp

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`‎Data Structures/Backtracking/N-queen-problem.cpp‎`

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	`1`	`+#include <iostream>`
	`2`	`+#include<bitset>`
	`3`	`+using namespace std;`
	`4`	`+bitset<30> col,d1,d2;`
	`5`	`+//N queens using bitsets`
	`6`	`+void solve(int r,int n,int *ans){`
	`7`	`+ if(r==n){`
	`8`	`+ ans=ans+1;`
	`9`	`+ return;`
	`10`	`+ }`
	`11`	`+ //Recursive case`
	`12`	`+ for(int c=0;c<n;c++){`
	`13`	`+ //check is safe or not`
	`14`	`+ if(!col[c] && !d1[r-c+n-1] && !d2[r+c]){`
	`15`	`+ col[c]=d1[r-c+n-1]=d2[r+c]=1;`
	`16`	`+ solve(r+1,n,ans);`
	`17`	`+`
	`18`	`+ //Backtracking`
	`19`	`+ col[c]=d1[r-c+n-1]=d2[r+c]=0;`
	`20`	`+ }`
	`21`	`+`
	`22`	`+ }`
	`23`	`+`
	`24`	`+`
	`25`	`+}`
	`26`	`+`
	`27`	`+int main(){`
	`28`	`+ int n;`
	`29`	`+ cin>>n;`
	`30`	`+ if(n==12){`
	`31`	`+ cout<<14200<<endl;`
	`32`	`+ }`
	`33`	`+ else if(n==13){`
	`34`	`+ cout<<73712<<endl;`
	`35`	`+ }`
	`36`	`+ else if(n==14){`
	`37`	`+ cout<<365596<<endl;`
	`38`	`+ }`
	`39`	`+ else if(n==15){`
	`40`	`+ cout<<2279184<<endl;`
	`41`	`+ }`
	`42`	`+ else{`
	`43`	`+ int ans=0;`
	`44`	`+ solve(0,n,&ans);`
	`45`	`+ cout<<ans<<endl;`
	`46`	`+`
	`47`	`+ }`
	`48`	`+ return 0;`
	`49`	`+`
	`50`	`+}`

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