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:
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root = [10,5,-3,3,2,null,11,3,-2,null,1], sum = 8
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/
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
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- 写一个函数pathSumFrom，表示从当前node开始向下查找
- 而pathSum表示的是，从这棵树中找。
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class {
public int pathSum(TreeNode root, int sum) {
if (root == null)
return 0;
return pathSumFrom(root, sum) + pathSum(root.left, sum) + pathSum(root.right, sum);
}
public int pathSumFrom(TreeNode root, int sum) {
if (root == null)
return 0;
return (sum == root.val ? 1: 0) + pathSumFrom(root.left, sum-root.val) + pathSumFrom(root.right, sum-root.val);
}
}
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