Create 377. Combination Sum IV

Author: rajatag03

377. Combination Sum IV

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+\\TLE DFS
+class Solution {
+    public int combinationSum4(int[] nums, int target) {
+        if(target==0){
+            return 1;
+        }
+        int res = 0;
+        for(int i:nums){
+            if(i<=target){
+                res+=combinationSum4(nums,target - i);
+            }
+        }
+        return res;
+    }
+}
+
+\\Top-down
+class Solution {
+    
+    int[] dp ;
+    public int combinationSum4(int[] nums, int target) {
+        
+        dp=new int[target+1];
+        Arrays.fill(dp,-1);
+        
+        dp[0] =1;
+        
+        helper(nums,target);
+        return dp[target];
+    }
+    
+    int helper(int[] nums,int target){
+        
+        if(dp[target]>-1){
+            return dp[target];
+        }
+        int res = 0;
+        for(int i:nums){
+            if(i<=target){
+                res+=helper(nums,target - i);
+            }
+        }
+        dp[target]=res;
+        return dp[target];
+    }
+}
+
+\\Bottom-up
+class Solution {
+    
+    int[] dp ;
+    public int combinationSum4(int[] nums, int target) {
+        
+        dp=new int[target+1];
+        
+        dp[0] =1;
+        
+        for(int i = 1 ; i<=target ;i++){
+            for(int n:nums){
+                if(i>=n){
+                    dp[i] += dp[i-n];
+                }
+            }
+        }
+        
+        return dp[target];
+    }
+}