feature/437: add a faster solution

leetcode/0437.Path-Sum-III/437. Path Sum III.go

@@ -39,3 +39,25 @@ func findPath437(root *TreeNode, sum int) int {
 	res += findPath437(root.Right, sum-root.Val)
 	return res
 }
+
+func pathSum(root *TreeNode, targetSum int) int {
+	prefixSum := make(map[int]int)
+	prefixSum[0] = 1
+	return dfs(root, prefixSum, 0, targetSum)
+}
+
+func dfs(root *TreeNode, prefixSum map[int]int, cur, sum int) int {
+	if root == nil {
+		return 0
+	}
+	cur += root.Val
+	cnt := 0
+	if v, ok := prefixSum[cur-sum]; ok {
+		cnt = v
+	}
+	prefixSum[cur]++
+	cnt += dfs(root.Left, prefixSum, cur, sum)
+	cnt += dfs(root.Right, prefixSum, cur, sum)
+	prefixSum[cur]--
+	return cnt
+}

leetcode/0437.Path-Sum-III/437. Path Sum III_test.go

@@ -45,7 +45,7 @@ func Test_Problem437(t *testing.T) {
 		_, p := q.ans437, q.para437
 		fmt.Printf("【input】:%v      ", p)
 		root := structures.Ints2TreeNode(p.one)
-		fmt.Printf("【output】:%v      \n", pathSumIII(root, p.sum))
+		fmt.Printf("【output】:%v      \n", pathSum(root, p.sum))
 	}
 	fmt.Printf("\n\n\n")
 }