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;
  }
 }