LeetCode 437. Path Sum III (路径之和之三)
You are given a binary tree in which each node contains an integer value.
Find the number of paths that sum to a given value.
The path does not need to start or end at the root or a leaf, but it must go downwards (traveling only from parent nodes to child nodes).
The tree has no more than 1,000 nodes and the values are in the range -1,000,000 to 1,000,000.
Example:
root = [10,5,-3,3,2,null,11,3,-2,null,1], sum = 8 10
/ \
5 -3
/ \ \
3 2 11
/ \ \
3 -2 1 Return 3. The paths that sum to 8 are: 1. 5 -> 3
2. 5 -> 2 -> 1
3. -3 -> 11
Java Solution:
Runtime beats 68.27%
完成日期:07/06/2017
关键词:Tree
关键点:利用两个递归functions来搜索从每一层level 各点开始到下面层次点的path值
/**
* Definition for a binary tree node.
* public class TreeNode {
* int val;
* TreeNode left;
* TreeNode right;
* TreeNode(int x) { val = x; }
* }
*/
public class Solution
{
int res = 0;
public int pathSum(TreeNode root, int sum)
{
if(root == null)
return res; traverseTree(root,sum); return res;
} public void traverseTree(TreeNode node, int sum)
{
if(node == null)
return; findPathSum(node, 0, sum);
traverseTree(node.left, sum);
traverseTree(node.right, sum); } public void findPathSum(TreeNode node, int path_sum, int sum)
{
if(node == null)
return; if(path_sum + node.val == sum)
res++; findPathSum(node.left, path_sum + node.val, sum);
findPathSum(node.right, path_sum + node.val, sum); }
}
参考资料:N/A
LeetCode 算法题目列表 - LeetCode Algorithms Questions List
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