Create 0494-target-sum.kt

Author: a93a

kotlin/0494-target-sum.kt

@@ -0,0 +1,18 @@
+class Solution {
+    fun findTargetSumWays(nums: IntArray, target: Int): Int {
+        val memo = HashMap<String, Int>()
+
+        fun dfs(i: Int, sum: Int): Int {
+            if (i == nums.size)
+                return if (sum == target) 1 else 0
+            val key = "$i:$sum"
+            if (key in memo)
+                return memo[key]!!
+            memo[key] = dfs(i + 1, sum + nums[i]) + 
+                dfs(i + 1, sum - nums[i])
+            return memo[key]!!
+        }
+
+        return dfs(0, 0)
+    }
+}