LeetCode-437. Path Sum III

LeetCode-437. Path Sum III

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 1Return 3. The paths that sum to 8 are:1. 5 -> 32. 5 -> 2 -> 13. -3 -> 11

题解：

class Solution {public: void getSum(TreeNode* t, int val, int sum, int &cnt) { if (t != NULL) { val += t->val; if (val == sum) { cnt++; } getSum(t->left, val, sum, cnt); getSum(t->right, val, sum, cnt); } } void preOrder(TreeNode* root, int sum, int &res) { if (root != NULL) { int cnt = 0; getSum(root, 0, sum, cnt); res += cnt; preOrder(root->left, sum, res); preOrder(root->right, sum, res); } } int pathSum(TreeNode* root, int sum) { int res = 0; preOrder(root, sum, res); return res; }};

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