描述
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
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
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分析
深度优先遍历二叉树。
解决方案1(Java)
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class Solution { public int pathSum(TreeNode root, int sum) { if (root == null) { return 0; } return dfs(root, sum) + pathSum(root.left, sum) + pathSum(root.right, sum); } private int dfs(TreeNode root, int sum) { if (root == null) { return 0; } if (root.val == sum) { return dfs(root.left, sum-root.val) + dfs(root.right, sum-root.val) + 1; } return dfs(root.left, sum-root.val) + dfs(root.right, sum-root.val); } }
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