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Code02_IsBST.java
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125 lines (110 loc) · 2.52 KB
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package class12;
import java.util.ArrayList;
public class Code02_IsBST {
public static class Node {
public int value;
public Node left;
public Node right;
public Node(int data) {
this.value = data;
}
}
public static boolean isBST1(Node head) {
if (head == null) {
return true;
}
ArrayList<Node> arr = new ArrayList<>();
in(head, arr);
for (int i = 1; i < arr.size(); i++) {
if (arr.get(i).value <= arr.get(i - 1).value) {
return false;
}
}
return true;
}
public static void in(Node head, ArrayList<Node> arr) {
if (head == null) {
return;
}
in(head.left, arr);
arr.add(head);
in(head.right, arr);
}
public static boolean isBST2(Node head) {
if (head == null) {
return true;
}
return process(head).isBST;
}
public static class Info {
public boolean isBST;
public int max;
public int min;
public Info(boolean i, int ma, int mi) {
isBST = i;
max = ma;
min = mi;
}
}
public static Info process(Node x) {
if (x == null) {
return null;
}
Info leftInfo = process(x.left);
Info rightInfo = process(x.right);
int max = x.value;
if (leftInfo != null) {
max = Math.max(max, leftInfo.max);
}
if (rightInfo != null) {
max = Math.max(max, rightInfo.max);
}
int min = x.value;
if (leftInfo != null) {
min = Math.min(min, leftInfo.min);
}
if (rightInfo != null) {
min = Math.min(min, rightInfo.min);
}
boolean isBST = true;
if (leftInfo != null && !leftInfo.isBST) {
isBST = false;
}
if (rightInfo != null && !rightInfo.isBST) {
isBST = false;
}
if (leftInfo != null && leftInfo.max >= x.value) {
isBST = false;
}
if (rightInfo != null && rightInfo.min <= x.value) {
isBST = false;
}
return new Info(isBST, max, min);
}
// 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 = 4;
int maxValue = 100;
int testTimes = 1000000;
for (int i = 0; i < testTimes; i++) {
Node head = generateRandomBST(maxLevel, maxValue);
if (isBST1(head) != isBST2(head)) {
System.out.println("Oops!");
}
}
System.out.println("finish!");
}
}