标签：parent pre des init lin nod integer value not
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
给定一颗二叉树，找出路径和等于sum的路径数。这里的路径是指从父节点到子节点的路径，不必一定是从根节点到叶子节点。马上想到深度优先搜索，但是要注意路径不一定从根节点开始。所以对于一个父节点来说，它所在路径上满足题设要求的路径，除了包括左右子树中路径和为sum-root->val的路径外，还应包括左右子树中路径和为sum的路径。
/** * 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 pathSum(TreeNode* root, int sum) { if(!root) return 0; return pathSum(root->left,sum)+pathSum(root->right,sum)+pathSumRoot(root,sum); } int pathSumRoot(TreeNode* root, int sum) { if(!root) return 0; int count=(sum==root->val?1:0); return pathSumRoot(root->left,sum-root->val)+ pathSumRoot(root->right,sum-root->val)+count; } };
标签：parent pre des init lin nod integer value not
原文地址：http://www.cnblogs.com/tacia/p/6290760.html
