LeetCode 404. Sum of Left Leaves (二叉树,递归)
2017-05-27 16:15
363 查看
Find the sum of all left leaves in a given binary tree.
Example:
输出二叉树左叶子节点的和。
思路:判断叶子节点的方法是,对于一个节点A,如果其左孩子和右孩子都不存在,则节点A是叶子节点。
进一步,判断左叶子节点:对于一个节点A的左孩子L,如果其左孩子和右孩子都不存在,则节点L是左叶子节点。
如果一个节点A的左孩子L是叶子节点,则返回节点L的值加上右子树的递归结果。
如果一个节点A的左孩子不是叶子节点(也就是左子树),则返回节点A的左右子树的递归结果之和。
/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
int sumOfLeftLeaves(TreeNode* root) {
if(root==NULL)return 0;
if(root->left!=NULL && root->left->left==NULL && root->left->right==NULL)//root的左孩子是叶节点
return root->left->val + sumOfLeftLeaves(root->right);
else return sumOfLeftLeaves(root->left) + sumOfLeftLeaves(root->right);
}
};
Example:
3 / \ 9 20 / \ 15 7 There are two left leaves in the binary tree, with values 9 and 15 respectively. Return 24.
输出二叉树左叶子节点的和。
思路:判断叶子节点的方法是,对于一个节点A,如果其左孩子和右孩子都不存在,则节点A是叶子节点。
进一步,判断左叶子节点:对于一个节点A的左孩子L,如果其左孩子和右孩子都不存在,则节点L是左叶子节点。
如果一个节点A的左孩子L是叶子节点,则返回节点L的值加上右子树的递归结果。
如果一个节点A的左孩子不是叶子节点(也就是左子树),则返回节点A的左右子树的递归结果之和。
/**
* Definition for a binary tree node.
* struct TreeNode {
* int val;
* TreeNode *left;
* TreeNode *right;
* TreeNode(int x) : val(x), left(NULL), right(NULL) {}
* };
*/
class Solution {
public:
int sumOfLeftLeaves(TreeNode* root) {
if(root==NULL)return 0;
if(root->left!=NULL && root->left->left==NULL && root->left->right==NULL)//root的左孩子是叶节点
return root->left->val + sumOfLeftLeaves(root->right);
else return sumOfLeftLeaves(root->left) + sumOfLeftLeaves(root->right);
}
};
相关文章推荐
- leetcode-404. Sum of Left Leaves 求左叶子节点的和,递归
- LeetCode 404. Sum of Left Leaves(二叉树)
- LeetCode 404. Sum of Left Leaves 递归终止条件
- LeetCode 404. Sum of Left Leaves
- [LeetCode]404. Sum of Left Leaves
- LeetCode 404. Sum of Left Leaves
- 【leetcode】404. Sum of Left Leaves【E】
- LeetCode 404. Sum of Left Leaves 解题报告
- leetcode-404. Sum of Left Leaves
- [leetcode] 404. Sum of Left Leaves
- LeetCode - 404. Sum of Left Leaves
- leetcode404. Sum of Left Leaves
- LeetCode—404. Sum of Left Leaves
- Leetcode 404. Sum of Left Leaves
- leetcode 404. Sum of Left Leaves
- 404. Sum of Left Leaves - leetcode
- LeetCode 404. Sum of Left Leaves (左子叶之和)
- LeetCode笔记:404. Sum of Left Leaves
- [leetcode: Python]404. Sum of Left Leaves
- Leetcode-标签为Tree 404. Sum of Left Leaves