Create Permutations.java

codewithcs · web-flow · commit cef6ffe19ddc · 2020-05-04T21:50:26.000+01:00
diff --git a/Medium/Permutations.java b/Medium/Permutations.java
@@ -0,0 +1,58 @@
+package AlgoExpert_Medium;
+
+import java.util.List;
+
+import java.util.ArrayList; 
+
+public class Permutations {
+	
+	public static void main(String[] args) {
+		List<Integer> array = new ArrayList<>() ;
+		array.add(1) ; array.add(2) ; array.add(3) ; 
+		System.out.println( getPermutations( array ) ) ; 
+	}
+	
+	public static List<List<Integer>> getPermutations(List<Integer> array) {
+	    
+		if(array.isEmpty()) {
+			return new ArrayList<List<Integer>>() ; 
+		}
+		
+		List<List<Integer>> list = new ArrayList<List<Integer>>() ;
+		
+		List<Integer> current = new ArrayList<>() ; 
+		
+		return permutations(array, current, list) ; 
+			
+	  }
+	
+	public static List<List<Integer>> permutations ( List<Integer> array, List<Integer> current, List<List<Integer>> list ) {
+
+		if(current.size() == array.size()) {
+			List<Integer> added = new ArrayList<>(current) ; // Imp to use new operator as current will be overwritten in subsequent calls.
+			list.add(added);
+			return list; 
+		}
+		
+		
+		for(int i=0 ; i<array.size(); i++) {
+			
+			int currentNumber = array.get(i) ;
+		
+			if(!current.contains(currentNumber)) { // Constraints. 
+					
+				current.add(currentNumber) ; // Choose
+					
+				permutations(array, current, list) ;  // Explore
+					
+				current.remove(current.size()-1) ; // Unchoose
+				
+			}
+				
+		}
+			
+		
+	 return list ; 
+		
+	}
+}
