leetcode -day17 Path Sum I II & Flatten Binary Tree to Linked List & Minimum Depth of Binary Tree

1、



Path Sum

Given a binary tree and a sum, determine if the tree has a root-to-leaf path such that adding up all the values along the path equals the given sum.

For example:

Given the below binary tree and <code>sum = 22</code>,

return true, as there exist a root-to-leaf path <code>5-&gt;4-&gt;11-&gt;2</code> which

sum is 22.

分析，此题比较简单，采用深度优先策略。

代码如下：

2、Path Sum II

Given a binary tree and a sum, find all root-to-leaf paths where each path‘s sum equals the given sum.

return

分析：此题也很简单，常见题，跟上述不同的是保存路径。

代码：

3、Flatten Binary Tree to Linked List

Given a binary tree, flatten it to a linked list in-place.

For example,

Given

The flattened tree should look like:

Hints:

If you notice carefully in the flattened tree, each node‘s right child points to the next node of a pre-order traversal.

分析：上述提示可以看出，相当于二叉树的先序遍历，对每一个结点，先访问根结点，再先序遍历左子树，串在根结点的右孩子上，再先序遍历原右子树，继续串在右孩子上。

4、Minimum Depth of Binary Tree

Given a binary tree, find its minimum depth.

The minimum depth is the number of nodes along the shortest path from the root node down to the nearest leaf node.

分析：此题很简单，递归。