Update 494_Target_Sum.java

Author: Sean Prashad

Dynamic Programming/494_Target_Sum.java

@@ -4,20 +4,26 @@ public int findTargetSumWays(int[] nums, int S) {
             return 0;
         }
 
-        return dfs(nums, S, 0, 0);
+        return dfs(nums, S, 0, 0, new HashMap<>());
     }
 
-    private int dfs(int[] nums, int S, int sum, int idx) {
+    private int dfs(int[] nums, int S, int sum, int idx, Map<String, Integer> m) {
+        String encodedVal = idx + "->" + sum;
+        if (m.containsKey(encodedVal)) {
+            return m.get(encodedVal);
+        }
+
         if (idx == nums.length) {
             if (sum == S) {
                 return 1;
             }
             return 0;
         }
 
-        int add = dfs(nums, S, sum + nums[idx], idx + 1);
-        int minus = dfs(nums, S, sum - nums[idx], idx + 1);
+        int add = dfs(nums, S, sum + nums[idx], idx + 1, m);
+        int minus = dfs(nums, S, sum - nums[idx], idx + 1, m);
 
+        m.put(encodedVal, add + minus);
         return add + minus;
     }
 }