剑指Offer之Java算法习题精讲二叉树专题篇下剑指Offer之Java算法习题精讲二

题目一
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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) {returnmethod(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

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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

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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

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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 list = new ArrayList(); public List 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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