Path Sum III
2017-05-01 15:09
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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
/ \ \
3 2 11
/ \ \
3 -2 1
Return 3. The paths that sum to 8 are:
5 -> 3
5 -> 2 -> 1
-3 -> 11
方法: DFS
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:
5 -> 3
5 -> 2 -> 1
-3 -> 11
方法: DFS
/** * 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 { private: int find(TreeNode* root,int temp_sum,int& sum){ if(root==NULL) return 0; int temp = temp_sum + root->val; return (temp==sum) + find(root->left,temp,sum) + find(root->right,temp,sum); } public: int pathSum(TreeNode* root, int sum) { if(root == NULL) return 0; return find(root,0,sum) + pathSum(root->left,sum) + pathSum(root->right,sum); } };
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