剑指Offer之Java算法习题精讲二叉树与N叉树

剑指Offer之Java算法习题精讲二叉树与N叉树

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 {

StringBuffer sb = new StringBuffer();

List list = new ArrayList();

public List binaryTreePaths(TreeNode root) {

method(root);

return list;

}

public void method(TreeNode root){

if(root==null) return;

int t = sb.length();

sb.append(root.val);

if(root.left==null&&root.right==null){

list.add(sb.toString());

}

sb.append("->");

method(root.lefhttp://t);

method(root.right);

sb.delete(t, sb.length());

}

}

题目二

解法

/**

* Definition for a binary tree node.

* public class TreeNode {

* int val;

* TreeNode left;

* TreeNOUEnZWfode 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 sumOfLeftLeaves(TreeNode root) {

method(root,false);

return ans;

}

public void method(TreeNode root,boolean flag){

if(root==null) return;

if(root.left==null&&root.right==null&&flag){

ans+=root.val;

return;

}

method(root.left,true);

method(root.right,false);

}

}

题目三

解法

/*

// Definition for a Node.

class Node {

public int val;

public List children;

public Node() {}

public Node(int _val) {

val = _val;

}

public Node(int _val, List _children) {

val = _val;

children = _children;

}

};

*/

class Solution {

public int maxDepth(Node root) {

if(root==null){

return 0;

}

int maxChildDepth = 0;

for(int i = 0;i

int childDepth = maxDepth(root.children.get(i));

maxChildDepth = Math.max(maxChildDepth, childDepth);

}

return maxChildDepth+1;

}

}

int childDepth = maxDepth(root.children.get(i));

maxChildDepth = Math.max(maxChildDepth, childDepth);

}

return maxChildDepth+1;

}

}

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