Java 二叉树
明天一定. 人气:0题目一
解法
/** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode() {} * TreeNode(int val) { this.val = val; } * TreeNode(int val, TreeNode left, TreeNode right) { * this.val = val; * this.left = left; * this.right = right; * } * } */ class Solution { public int maxDepth(TreeNode root) { return method(root); } int method(TreeNode root){ if(root==null){ return 0; } int l = method(root.left); int r = method(root.right); return Math.max(l, r) + 1; } }
题目二
解法
/** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode() {} * TreeNode(int val) { this.val = val; } * TreeNode(int val, TreeNode left, TreeNode right) { * this.val = val; * this.left = left; * this.right = right; * } * } */ class Solution { int ans = 0; public int diameterOfBinaryTree(TreeNode root) { method(root); return ans; } public int method(TreeNode root){ if(root==null){ return 0; } int l = method(root.left); int r = method(root.right); ans = Math.max(ans,l+r); return Math.max(l,r)+1; } }
题目三
解法
/** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode() {} * TreeNode(int val) { this.val = val; } * TreeNode(int val, TreeNode left, TreeNode right) { * this.val = val; * this.left = left; * this.right = right; * } * } */ class Solution { public int minDepth(TreeNode root) { if(root==null) return 0; if(root.left==null&&root.right==null) return 1; int min = Integer.MAX_VALUE; if(root.left!=null){ min = Math.min(min,minDepth(root.left)); } if(root.right!=null){ min = Math.min(min,minDepth(root.right)); } return min+1; } }
题目四
解法
/** * Definition for a binary tree node. * public class TreeNode { * int val; * TreeNode left; * TreeNode right; * TreeNode() {} * TreeNode(int val) { this.val = val; } * TreeNode(int val, TreeNode left, TreeNode right) { * this.val = val; * this.left = left; * this.right = right; * } * } */ class Solution { List<Integer> list = new ArrayList<Integer>(); public List<Integer> preorderTraversal(TreeNode root) { method(root); return list; } public void method(TreeNode root){ if(root==null){ return; } // 前序 list.add(root.val); method(root.left); // 中序 method(root.right); // 后序 } }
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