add new solutions

solutions/4/q437/solution.go

@@ -0,0 +1,36 @@
+package q437
+
+type TreeNode struct {
+	Val   int
+	Left  *TreeNode
+	Right *TreeNode
+}
+
+func count(node *TreeNode, prefix []int, target int) int {
+	if node == nil {
+		return 0
+	}
+	if len(prefix) > 0 {
+		prefix = append(prefix, node.Val+prefix[len(prefix)-1])
+	} else {
+		prefix = append(prefix, node.Val)
+	}
+
+	cnt := 0
+	for i := range len(prefix) - 1 {
+		if prefix[len(prefix)-1]-prefix[i] == target {
+			cnt++
+		}
+	}
+	if prefix[len(prefix)-1] == target {
+		cnt++
+	}
+
+	return cnt + count(node.Left, prefix, target) + count(node.Right, prefix, target)
+}
+
+func pathSum(root *TreeNode, targetSum int) int {
+	return count(root, nil, targetSum)
+}
+
+var _ = pathSum