backtracking advanced

Author: Mohit Jain

StringPermutation

@@ -0,0 +1,50 @@
+#include <bits/stdc++.h>
+#include <string>
+
+using namespace std;
+void permute(char *in, int i, set<string> &s) {
+	// base case
+     
+     if(in[i] == '\0') {
+     	
+     	// cout<<in<<endl;
+     	string gd(in);
+     	s.insert(gd);
+     	return;
+
+     } 
+
+     for (int j = i; in[j]!= '\0';j++){
+        
+        swap(in[i],in[j]);
+        permute(in,i+1,s);
+
+        // Backtracking - to restore the 
+        // original array
+
+        swap(in[i],in[j]);
+     }
+
+
+
+	
+}
+
+int main() {
+     
+     #ifndef ONLINE_JUDGE
+    // for getting input from input.txt
+    freopen("input.txt", "r", stdin);
+    // for writing output to output.txt
+    freopen("output.txt", "w", stdout);
+    #endif
+    
+    set<string> s;
+	char in[100]; 
+	cin >> in;
+	
+   permute(in,0,s);
+
+   for(auto str: s){ cout<<str<<",";}
+	return 0;
+}

StringPermutation.cpp

@@ -1 +1 @@
-123
+4

input.txt

@@ -0,0 +1,87 @@
+#include <bits/stdc++.h>
+
+using namespace std;
+
+bool isSafe(int board[][10], int i, int j
+	, int n) {
+	for(int row =0; row<i; row++){
+		if(board[row][j] == 1){
+			return false;
+		}
+	}
+	int x = i;
+	int y = j;
+
+	while (x >=0 and y>=0){
+		if(board[x][y] == 1) {
+			return false;
+		}
+		x--; 
+		y--;
+	}
+
+		 x = i;
+	       y = j;
+
+	while (x >=0 and y<n){
+		if(board[x][y] == 1) {
+			return false;
+		}
+		x--; 
+		y++;
+	}
+	return true;
+}
+bool solvedQueen(int board[][10],int i, 
+	int n) {
+	// Base Case
+	if(i == n) {
+      
+      for(int i = 0; i<n;i++) {
+      	for(int j=0; j< n; j ++) {
+      		if(board[i][j] == 1){
+      			cout<<" Q ";
+      		}
+      		else {
+      			cout<< " . ";
+      		}
+      	}
+      	cout<<endl;
+      }
+      cout<<endl<<endl;
+      return false;
+	}
+	// rec case 
+	// Try to place queen in current row
+	for(int j=0; j <n; j++){
+      if(isSafe(board,i,j,n)){
+      	board[i][j] = 1;
+       bool nextQueenRakhPaye = 
+       solvedQueen(board,i+1,n);
+       if(nextQueenRakhPaye) {
+       	return true;
+       }
+       board[i][j] = 0;
+      }
+
+	}
+     return false;
+}
+
+int main() {
+   
+
+     #ifndef ONLINE_JUDGE
+    // for getting input from input.txt
+    freopen("input.txt", "r", stdin);
+    // for writing output to output.txt
+    freopen("output.txt", "w", stdout);
+    #endif
+   int n;
+    cin>>n;
+   int board[10][10] = {0};
+   
+   solvedQueen(board,0,n);
+
+   return 0 ; 
+}

nQueen

@@ -0,0 +1,107 @@
+#include <bits/stdc++.h>
+
+using namespace std;
+
+bool isSafe(int board[][10], int i, int j
+	, int n) {
+	for(int row =0; row<i; row++){
+		if(board[row][j] == 1){
+			return false;
+		}
+	}
+	int x = i;
+	int y = j;
+
+	while (x >=0 and y>=0){
+		if(board[x][y] == 1) {
+			return false;
+		}
+		x--; 
+		y--;
+	}
+
+		 x = i;
+	       y = j;
+
+	while (x >=0 and y<n){
+		if(board[x][y] == 1) {
+			return false;
+		}
+		x--; 
+		y++;
+	}
+	return true;
+}
+bool solvedQueen(int board[][10],int i, 
+	int n) {
+	// Base Case
+	if(i == n) {
+      
+      for(int i = 0; i<n;i++) {
+      	for(int j=0; j< n; j ++) {
+      		if(board[i][j] == 1){
+      			cout<<" Q ";
+      		}
+      		else {
+      			cout<< " . ";
+      		}
+      	}
+      	cout<<endl;
+      }
+      cout<<endl<<endl;
+      return false;
+	}
+	// rec case 
+	// Try to place queen in current row
+	for(int j=0; j <n; j++){
+      if(isSafe(board,i,j,n)){
+      	board[i][j] = 1;
+       bool nextQueenRakhPaye = 
+       solvedQueen(board,i+1,n);
+       if(nextQueenRakhPaye) {
+       	return true;
+       }
+       board[i][j] = 0;
+      }
+
+	}
+     return false;
+}
+    bitset<30> col,d1,d2;
+
+void solve(int r, int n, int &ans
+	  ) {
+	if(r== n) {
+		ans++;
+		return;
+	}
+	for(int c=0; c<n;c++){
+		if(!col[c] and !d1[r-c + n-1]
+			and !d2[r+c]){
+			col[c] = d1[r-c+n-1] = 
+		    d2[r+c] = 1;
+		    solve(r+1,n,ans);
+		    col[c] = d1[r-c+n-1] = 
+		    d2[r+c] = 0;
+		}
+	}
+}
+int main() {
+   
+
+     #ifndef ONLINE_JUDGE
+    // for getting input from input.txt
+    freopen("input.txt", "r", stdin);
+    // for writing output to output.txt
+    freopen("output.txt", "w", stdout);
+    #endif
+   int n;
+    cin>>n;
+   int board[10][10] = {0};
+   int ans = 0;
+   solve(0,n,ans);
+   cout<<ans<<endl;
+   // solvedQueen(board,0,n);
+
+   return 0 ; 
+}

nQueen.cpp

@@ -1,15 +1 @@
-1 1 0 0 
-0 1 0 0 
-0 1 1 0 
-0 0 1 1 
-
-1 0 0 0 
-1 1 0 0 
-0 1 1 0 
-0 0 1 1 
-
-1 0 0 0 
-1 0 0 0 
-1 1 1 0 
-0 0 1 1 
-
+2