路径总和

             5
            / \
           4   8
          /   / \
         11  13  4
        /  \      \
       7    2      1

package main

import "fmt"

type TreeNode struct {
    Val   int
    Left  *TreeNode
    Right *TreeNode
}

func main() {
    fmt.Println(hasPathSum(&TreeNode{
        Val: 5,
        Left: &TreeNode{
            Val: 4,
            Left: &TreeNode{
                Val: 11,
                Left: &TreeNode{
                    Val: 7,
                },
                Right: &TreeNode{
                    Val: 2,
                },
            },
        },
        Right: &TreeNode{
            Val: 8,
            Left: &TreeNode{
                Val: 13,
            },
            Right: &TreeNode{
                Val: 4,
                Right: &TreeNode{
                    Val: 1,
                },
            },
        },
    }, 22))
}

//给定一个二叉树和一个目标和，判断该树中是否存在根节点到叶子节点的路径，这条路径上所有节点值相加等于目标和。
func hasPathSum(root *TreeNode, sum int) bool {
    if root == nil {
        return false
    }
    if root.Val == sum && root.Right == nil && root.Left == nil {
        return true
    }
    if hasPathSum(root.Left, sum-root.Val) {
        return true
    }
    if hasPathSum(root.Right, sum-root.Val) {
        return true
    }
    return false
}