题目
给定一棵树二叉树的头节点head，返回这颗二叉树是不是平衡二叉树
思路
代码
public class Code03_IsBalanced {
public static class Node {
public int value;
public Node left;
public Node right;
public Node(int data) {
this.value = data;
}
}
public static boolean isBalanced1(Node head) {
boolean[] ans = new boolean[1];
ans[0] = true;
process1(head, ans);
return ans[0];
}
public static int process1(Node head, boolean[] ans) {
if (!ans[0] || head == null) {
return -1;
}
int leftHeight = process1(head.left, ans);
int rightHeight = process1(head.right, ans);
if (Math.abs(leftHeight - rightHeight) > 1) {
ans[0] = false;
}
return Math.max(leftHeight, rightHeight) + 1;
}
public static boolean isBalanced2(Node head) {
return process(head).isBalanced;
}
public static class Info{
public boolean isBalanced;
public int height;
public Info(boolean i, int h) {
isBalanced = i;
height = h;
}
}
public static Info process(Node x) {
if(x == null) {
return new Info(true, 0);
}
Info leftInfo = process(x.left);
Info rightInfo = process(x.right);
int height = Math.max(leftInfo.height, rightInfo.height) + 1;
boolean isBalanced = true;
if(!leftInfo.isBalanced) {
isBalanced = false;
}
if(!rightInfo.isBalanced) {
isBalanced = false;
}
if(Math.abs(leftInfo.height - rightInfo.height) > 1) {
isBalanced = false;
}
return new Info(isBalanced, height);
}
// for test
public static Node generateRandomBST(int maxLevel, int maxValue) {
return generate(1, maxLevel, maxValue);
}
// for test
public static Node generate(int level, int maxLevel, int maxValue) {
if (level > maxLevel || Math.random() < 0.5) {
return null;
}
Node head = new Node((int) (Math.random() * maxValue));
head.left = generate(level + 1, maxLevel, maxValue);
head.right = generate(level + 1, maxLevel, maxValue);
return head;
}
public static void main(String[] args) {
int maxLevel = 5;
int maxValue = 100;
int testTimes = 1000000;
for (int i = 0; i < testTimes; i++) {
Node head = generateRandomBST(maxLevel, maxValue);
if (isBalanced1(head) != isBalanced2(head)) {
System.out.println("Oops!");
}
}
System.out.println("finish!");
}
}