2.3二叉樹(shù)的存儲(chǔ)

// 孩子表示法
class Node {
int val; // 數(shù)據(jù)域
Node left; // 左孩子的引用，常常代表左孩子為根的整棵左子樹(shù)
Node right; // 右孩子的引用，常常代表右孩子為根的整棵右子樹(shù)
}
// 孩子雙親表示法
class Node {
int val; // 數(shù)據(jù)域
Node left; // 左孩子的引用，常常代表左孩子為根的整棵左子樹(shù)
Node right; // 右孩子的引用，常常代表右孩子為根的整棵右子樹(shù)
Node parent; // 當(dāng)前節(jié)點(diǎn)的根節(jié)點(diǎn)
}

1.手動(dòng)快速創(chuàng)建一棵簡(jiǎn)單的二叉樹(shù)

?

public Node TreeBuild(){Node node1 = new Node('A');Node node2 = new Node('B');Node node3 = new Node('C');Node node4 = new Node('D');Node node5 = new Node('E');Node node6 = new Node('F');Node node7 = new Node('G');Node node8 = new Node('H');Node node9 = new Node('I');Node node10 = new Node('J');Node node11 = new Node('K');node1.left = node2;node1.right = node3;node2.left = node4;node2.right = node5;node3.left = node6;node3.right = node7;node4.left = node8;node4.right = node9;node5.right = node10;node6.right = node11;return node1;}

·   //前序遍歷public void preOrder(Node root){if(root == null){return ;}System.out.print(root.val+" ");preOrder(root.left);preOrder(root.right);}//中序遍歷public void inOrder(Node root){if(root == null){return;}inOrder(root.left);System.out.print(root.val+" ");inOrder(root.right);}//后序遍歷public void postOrder(Node root){if(root == null){return;}postOrder(root.left);postOrder(root.right);System.out.print(root.val+" ");}

    //層序遍歷public List<List<Character>> levelOrder(Node root){//創(chuàng)建一個(gè)二維數(shù)組保存每一層的元素List<List<Character>> list = new ArrayList<>();if(root == null){return list;}//臨時(shí)隊(duì)列Deque<Node> deque = new LinkedList<>();//頭節(jié)點(diǎn)放入隊(duì)列deque.offer(root);//隊(duì)列非空進(jìn)循環(huán)while(!deque.isEmpty()){int size = deque.size();List<Character> curList = new ArrayList<>();for (int i = 0; i < size; i++){Node x = deque.pop();//左子樹(shù)不為空，左子樹(shù)入隊(duì)列if(x.left != null){deque.offer(x.left);}//右子樹(shù)不為空，右子樹(shù)入隊(duì)列if(x.right != null){deque.offer(x.right);}//出棧的元素值存放在臨時(shí)數(shù)組里curList.add(x.val);}//出循環(huán)將臨時(shí)數(shù)組加入二維數(shù)組list.add(curList);}return list;}

4.獲取樹(shù)中節(jié)點(diǎn)的個(gè)數(shù)

    public int size(Node root){if(root == null){return 0;}return 1 + size(root.left) + size(root.right);}

5.獲取葉子節(jié)點(diǎn)的個(gè)數(shù)

    // 獲取葉子節(jié)點(diǎn)的個(gè)數(shù)int getLeafNodeCount(Node root){if(root == null){return 0;}if(root.left == null && root.right == null){return 1;}return getLeafNodeCount(root.left) + getLeafNodeCount(root.right);}

6.獲取第K層節(jié)點(diǎn)的個(gè)數(shù)

    // 獲取第K層節(jié)點(diǎn)的個(gè)數(shù)int getKLevelNodeCount(Node root,int k){if(root == null || k <= 0){return 0;}if(k == 1){return 1;}return getKLevelNodeCount(root.left,k-1) + getKLevelNodeCount(root.right,k-1);}

7.獲取二叉樹(shù)的高度

    // 獲取二叉樹(shù)的高度int getHeight(Node root){if(root == null){return 0;}return 1 + Math.max(getHeight(root.left),getHeight(root.right));}

8.檢測(cè)值為value的元素是否存在

    // 檢測(cè)值為value的元素是否存在public boolean find(Node root, int val){if(root == null){return false;}if(root.val == val){return true;}return find(root.left,val) || find(root.right,val);}

9.判斷一棵樹(shù)是不是完全二叉樹(shù)

    // 判斷一棵樹(shù)是不是完全二叉樹(shù)boolean isCompleteTree(Node root){if(root == null){return true;}//隊(duì)列為空出循環(huán)，兩個(gè)階段//1.所有都是度為2的節(jié)點(diǎn)//2.碰到第一個(gè)度為1的節(jié)點(diǎn)，右節(jié)點(diǎn)直接false,左節(jié)點(diǎn)進(jìn)入第二階段//碰到第一個(gè)度為0的節(jié)點(diǎn)，進(jìn)入第二階段//3。第二階段，都是葉子節(jié)點(diǎn)，如果有不是葉子節(jié)點(diǎn)，直接falseDeque<Node> deque = new LinkedList<>();deque.offer(root);boolean flag = true;while(!deque.isEmpty()){if(flag){Node x = deque.poll();if(x.left != null && x.right != null){deque.offer(x.left);deque.offer(x.right);}else if(x.right != null){return false;}else if(x.left != null){deque.offer(x.left);flag = false;}else {flag = false;}}else {Node x = deque.poll();if(x.left != null || x.right != null){return false;}}}return true;}