LeetCode:437. Path Sum III(查詢最大值)
阿新 • • 發佈:2018-12-10
ou 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
方法1:(利用深度優先演算法)
/** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode(int x) { val = x; } * } */ 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; int res = 0; if(root.val == sum) res++; res += dfs(root.left, sum - root.val); res += dfs(root.right, sum - root.val); return res; } }
時間複雜度:O(n^2)
空間複雜度:O(n)