Add Three Sum Problem (TheAlgorithms#2741)

Author: Sneha421

Misc/ThreeSumProblem.java

@@ -0,0 +1,109 @@
+import java.util.*;
+public class ThreeSumProblem {
+	public static void main(String args[])
+	{
+		Scanner scan = new Scanner(System.in);
+		System.out.print("Enter the target sum ");
+		int ts= scan.nextInt();
+		System.out.print("Enter the number of elements in the array ");
+		int n = scan.nextInt();
+		System.out.println("Enter all your array elements:");
+		int arr[]= new int[n];
+		for(int i=0;i<n;i++)
+		{ 
+			arr[i]=scan.nextInt();
+		}
+		ThreeSumProblem th = new ThreeSumProblem();
+		System.out.println("Brute Force Approach\n"+(th.BruteForce(arr,ts))+"\n");
+		System.out.println("Two Pointer Approach\n"+(th.TwoPointer(arr,ts))+"\n");
+		System.out.println("Hashmap Approach\n"+(th.Hashmap(arr,ts)));
+
+}
+	public List<List<Integer>> BruteForce(int[] nums,int target) {
+        List<List<Integer>> arr = new ArrayList<List<Integer>>();
+       
+        for(int i=0;i<nums.length;i++)
+        {
+             for(int j=i+1;j<nums.length;j++)
+             {
+                  for(int k=j+1;k<nums.length;k++)
+                  {
+                         if(nums[i]+nums[j]+nums[k]==target)
+                         {  List<Integer> temp = new ArrayList<>();
+                            temp.add(nums[i]);
+                            temp.add(nums[j]);
+                            temp.add(nums[k]);
+                            Collections.sort(temp);
+                            arr.add(temp);
+                         }
+                                 
+                             
+                      }
+                  }
+             }
+        arr = new ArrayList<List<Integer>>(new LinkedHashSet<List<Integer>>(arr));
+        return arr;
+        }
+	public List<List<Integer>> TwoPointer(int[] nums, int target) {
+		 Arrays.sort(nums);
+	        List<List<Integer>> arr = new ArrayList<List<Integer>>();
+	        int start=0;
+	        int end=0;
+	        int i = 0;
+	        while(i<nums.length-1)
+	        {
+	            start=i+1;
+	            end=nums.length-1;
+	            while (start<end)
+	            {
+	                if (nums[start]+nums[end]+nums[i]==target)
+	                {
+	                    List<Integer> temp = new ArrayList<>();
+	                            temp.add(nums[i]);
+	                            temp.add(nums[start]);
+	                            temp.add(nums[end]);
+	                            arr.add(temp);
+	                            start++;
+	                            end--;
+	                }
+	                else if (nums[start]+nums[end]+nums[i]<target)
+	                    start+=1;
+	                else
+	                    end-=1;
+	                    
+	            }
+	            i++;
+	        }
+	        Set<List<Integer>> set = new LinkedHashSet<List<Integer>>(arr);
+			return new ArrayList<List<Integer>>(set);
+	}
+	public List<List<Integer>> Hashmap(int[] nums, int target) {
+		 Arrays.sort(nums);
+	        Set<List<Integer>> ts = new HashSet();
+	        HashMap<Integer,Integer> hm = new HashMap<>();
+	        
+	        for(int i=0;i<nums.length;i++)
+	        {
+	            hm.put(nums[i],i);
+	        }
+	        
+	        for(int i=0;i<nums.length;i++)
+	        {
+	            for(int j=i+1;j<nums.length;j++)
+	            {
+	                int t= target - nums[i] - nums[j];
+	                if(hm.containsKey(t) && hm.get(t)>j)
+	                {
+	                     List<Integer> temp = new ArrayList<>();
+		                            temp.add(nums[i]);
+		                            temp.add(nums[j]);
+		                            temp.add(t);
+		                            ts.add(temp);
+	                }
+	            }
+	        }
+	        return new ArrayList(ts);
+	}
+	
+}
+

Misc/TwoSumProblem.java

@@ -1,5 +1,4 @@
 package Misc;
-
 import java.util.*;
 import java.util.stream.Collectors;