added java program

Java/Program-21/K_Equal_Sum_Subset.java

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+public class K_Equal_Sum_Subset {
+    //helper function
+    boolean helpInPartition(int nums[],boolean visited[],int start,int k,int currentSum,int targetSum)
+    {
+        //when there are no more subsets left to make
+        if(k==0)
+            return true;
+        if(currentSum>targetSum)
+            return false;
+        //if current sum equals target sum,we are left with k-1 subsets to make
+        if(currentSum==targetSum)
+            return helpInPartition(nums,visited,0,k-1,0,targetSum);
+        for(int j=start;j<nums.length;j++)
+        {
+            //if nums[j] is already included in a subset skip this iteration
+            if(visited[j])
+                continue;
+            //let us assume nums[j] is a part of the current subset
+            visited[j]=true;
+            //current sum < target sum,we look for elements beyond j
+            if(helpInPartition(nums,visited,j+1,k,currentSum+nums[j],targetSum))
+                return true;
+            //if nums[j] is not a part of the current subset , we mark it unvisited
+            visited[j]=false;
+        }
+        return false;
+    }
+    public boolean canPartitionKSubsets(int[] nums, int k) {
+        int sum=0;
+        for(int i:nums)
+            sum+=i;
+        //nums can be divided into k equal sum subsets only if the sum of its elements is divisible by k
+        if(sum%k!=0)
+            return false;
+        //visited array to keep track where an element is already a part of a subset or not
+        boolean visited[]=new boolean[nums.length];
+        return helpInPartition(nums,visited,0,k,0,sum/k);
+    }
+}

Java/Program-21/readme.md

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+Program 21
+
+Program to Partition to K Equal Sum Subsets
+
+Given an integer array nums and an integer k, return true if it is possible to divide this array into k non-empty subsets whose sums are all equal.
+
+Example 1:
+
+Input: nums = [4,3,2,3,5,2,1], k = 4
+Output: true
+Explanation: It's possible to divide it into 4 subsets (5), (1, 4), (2,3), (2,3) with equal sums.