Java与算法（12）

Java与算法（12）

1.二叉树节点间最大距离问题

给定头节点，求最大距离

public class MaxDIstance {
	public static class Node {
		public int value;
		public Node left;
		public Node right;

		public Node(int data) {
			this.value = data;
		}
	}

	public static int maxDistance(Node head) {
		int[] record = new int[1];
		return posOrder(head, record);
	}

	public static int posOrder(Node head, int[] record) {
		if (head == null) {
			record[0] = 0;
			return 0;
		}
		int lMax = posOrder(head.left, record);
		int maxfromLeft = record[0];
		int rMax = posOrder(head.right, record);
		int maxFromRight = record[0];
		int curNodeMax = maxfromLeft + maxFromRight + 1;
		record[0] = Math.max(maxfromLeft, maxFromRight) + 1;
		return Math.max(Math.max(lMax, rMax), curNodeMax);
	}

	public static void main(String[] args) {
		Node head1 = new Node(1);
		head1.left = new Node(2);
		head1.right = new Node(3);
		head1.left.left = new Node(4);
		head1.left.right = new Node(5);
		head1.right.left = new Node(6);
		head1.right.right = new Node(7);
		head1.left.left.left = new Node(8);
		head1.right.left.right = new Node(9);
		System.out.println(maxDistance(head1));
	}

}

2.找出两个节点的最近公共祖先

public class LowAncestor {

	public static class Node {
		public int value;
		public Node left;
		public Node right;

		public Node(int data) {
			this.value = data;
		}
	}
	
	public static Node lowestAncestor(Node head, Node o1, Node o2) {
		if (head == null || head == o1 || head == o2) {
			return head;
		}
		Node left = lowestAncestor(head.left, o1, o2);
		Node right = lowestAncestor(head.right, o1, o2);
		if (left != null && right != null) {
			return head;
		}
		return left != null ? left : right;
	}

	public static void main(String[] args) {
		Node head = new Node(1);
		head.left = new Node(2);
		head.right = new Node(3);
		head.left.left = new Node(4);
		head.left.right = new Node(5);
		head.right.left = new Node(6);
		head.right.right = new Node(7);
		head.right.right.left = new Node(8);
		Node o1 = head.left.right;
		Node o2 = head.right.left;

		
		System.out.println("o1 : " + o1.value);
		System.out.println("o2 : " + o2.value);
		System.out.println("ancestor : " + lowestAncestor(head, o1, o2).value);
		

		
		
	}

}

3.在二叉树找到一个节点的后继节点

public class GetNextNode {
	public static class Node {
		public int value;
		public Node left;
		public Node right;
		public Node parent;

		public Node(int data) {
			this.value = data;
		}
	}
	public static Node getNextNode(Node node) {
		if (node == null) {
			return node;
		}
		if (node.right != null) {
			return getLeftMost(node.right);
		} else {
			Node parent = node.parent;
			while (parent != null && parent.left != node) {
				node = parent;
				parent = node.parent;
			}
			return parent;
		}
	}

	public static Node getLeftMost(Node node) {
		if (node == null) {
			return node;
		}
		while (node.left != null) {
			node = node.left;
		}
		return node;
	}
	
	
	
	public static void main(String[] args) {
		Node head = new Node(6);
		head.parent = null;
		head.left = new Node(3);
		head.left.parent = head;
		head.left.left = new Node(1);
		head.left.left.parent = head.left;
		head.left.left.right = new Node(2);
		head.left.left.right.parent = head.left.left;
		head.left.right = new Node(4);
		head.left.right.parent = head.left;
		head.left.right.right = new Node(5);
		head.left.right.right.parent = head.left.right;
		head.right = new Node(9);
		head.right.parent = head;
		head.right.left = new Node(8);
		head.right.left.parent = head.right;
		head.right.left.left = new Node(7);
		head.right.left.left.parent = head.right.left;
		head.right.right = new Node(10);
		head.right.right.parent = head.right;
		Node test = head.left.right.right;
		Node node = getNextNode(test);
		System.out.println(node.value);
		
		
	}

}