題目來源：112. 路徑總和

給你二叉樹的根節點root和一個表示目標和的整數targetSum，判斷該樹中是否存在根節點到葉子節點的路徑，這條路徑上所有節點值相加等於目標和targetSum。

葉子節點是指沒有子節點的節點。

示例 1：

輸入：root = [5,4,8,11,null,13,4,7,2,null,null,null,1], targetSum = 22
輸出：true

示例 2：

輸入：root = [1,2,3], targetSum = 5
輸出：false

示例 3：

輸入：root = [1,2], targetSum = 0
輸出：false

遞迴

/*
 
*
 * Definition for a binary tree node.
 * function TreeNode(val, left, right) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.left = (left===undefined ? null : left)
 *     this.right = (right===undefined ? null : right)
 * }
 */
/**
 * @param {TreeNode} root
 * @param {number} targetSum
 * @return {boolean}
 
 
*/
var hasPathSum = function(root, targetSum) {
  if(!root){
    return false
  }
  const sum = targetSum - root.val
  if(!root.left && !root.right){
    return sum === 0
  }
  return hasPathSum(root.left, sum) || hasPathSum(root.right, sum)
};

廣度優先

/**
 * Definition for a binary tree node.
 * function TreeNode(val, left, right) {
 *     this.val = (val===undefined ? 0 : val)
 *     this.left = (left===undefined ? null : left)
 *     this.right = (right===undefined ? null : right)
 * }
 
 
*/
/**
 * @param {TreeNode} root
 * @param {number} targetSum
 * @return {boolean}
 */
var hasPathSum = function(root, targetSum) {
  if(!root){
    return false
  }

  var stack = []
  var val = []
  stack.push([root])
  val.push([targetSum])
  while(stack.length){
    let level = stack.shift()
    let levelVal = val.shift()
    let len = level.length
    let stackTmp = []
    let valTmp = []
    for(let i = 0;i < len; i++){
      let node = level[i]
      if(!node){
        continue
      }
      let nodeVal = levelVal[i]
      if(!node.left && !node.right){
        if((nodeVal - node.val) == 0 ){
          return true;
        }
        continue
      }
      if(node.left){
        stackTmp.push(node.left)
        valTmp.push(nodeVal - node.val)
      }
      if(node.right){
        stackTmp.push(node.right)
        valTmp.push(nodeVal - node.val)
      }
    }
    if(stackTmp.length)stack.push(stackTmp)
    if(valTmp.length)val.push(valTmp)
  }
  return false
};

Python3

# Definition for a binary tree node.
# class TreeNode:
#     def __init__(self, val=0, left=None, right=None):
#         self.val = val
#         self.left = left
#         self.right = right
class Solution:
    def hasPathSum(self, root: TreeNode, targetSum: int) -> bool:
        if not root:
            return False
        sum = targetSum - root.val
        if not root.left and not root.right:
            return sum == 0
        left  = self.hasPathSum(root.left , sum)
        right = self.hasPathSum(root.right, sum)
        return left or right

廣度優先

class Solution:
    def hasPathSum(self, root: TreeNode, targetSum: int) -> bool:
        if not root:
            return False
        stack = list()
        stack.append([(targetSum, root)])

        while stack:
          level = stack.pop(0)
          tmp = list()
          for node in level:
            if not node[1]:
              continue
            if not node[1].left and not node[1].right:
              if node[0] == node[1].val:
                return True
            if node[1].left:
              tmp.append((node[0] - node[1].val, node[1].left))
            if node[1].right:
              tmp.append((node[0] - node[1].val, node[1].right))
          if tmp:
            stack.append(tmp)
        return False

提示：

• 樹中節點的數目在範圍[0, 5000]內
• -1000 <= Node.val <= 1000
• -1000 <= targetSum <= 1000