public class TestBinaryTree {
static class TreeNode {
public char val;
public TreeNode left;
public TreeNode right;
public TreeNode(char val) {
this.val = val;
}
}
public TreeNode createTree() {
TreeNode A = new TreeNode('A');
TreeNode B = new TreeNode('B');
TreeNode C = new TreeNode('C');
TreeNode D = new TreeNode('D');
TreeNode E = new TreeNode('E');
TreeNode F = new TreeNode('F');
TreeNode G = new TreeNode('G');
TreeNode H = new TreeNode('H');
A.left = B;
A.right = C;
B.left = D;
B.right = E;
C.left = F;
C.right = G;
E.right = H;
return A;
}
}
java复制代码
public class Test {
public static void main(String[] args) {
TestBinaryTree testBinaryTree = new TestBinaryTree();
TestBinaryTree.TreeNode root = testBinaryTree.createTree();
}
}
public int size(TreeNode root) {
if (root == null) {
return 0;
}
int ret = size(root.left) + size(root.right) + 1;
return ret;
}
获取叶子节点的个数
整棵树的叶子节点个数=左子树的叶子节点+右子树的叶子节点
java复制代码
public int getLeafNodeCount(TreeNode root) {
if (root == null) {
return 0;
}
if (root.left == null && root.right == null) {
return 1;
}
return getLeafNodeCount(root.left) + getLeafNodeCount(root.right);
}
获取第K层节点的个数
java复制代码
public int getKLevelNodeCount(TreeNode root, int k) {
if (root == null) {
return 0;
}
if (k == 1) {
return 1;
}
return getKLevelNodeCount(root.left, k - 1) + getKLevelNodeCount(root.right, k - 1);
}
获取二叉树的高度
整棵树的高度=Math.max(左树高度和右树高度)+1
java复制代码
public int getHeight(TreeNode root) {
if (root == null) {
return 0;
}
int leftHeight = getHeight(root.left);
int rightHeight = getHeight(root.right);
return leftHeight > rightHeight ? leftHeight + 1 : rightHeight + 1;
}
检测值为value的元素是否存在
java复制代码
TreeNode find(TreeNode root, int val) {
if (root == null) {
return null;
}
if (root.val == val) {
return root;
}
TreeNode ret = find(root.left, val);
if (ret != null) {
return ret;
}
ret = find(root.right, val);
if (ret != null) {
return ret;
}
return null;
}
层序遍历
java复制代码
void levelOrder(TreeNode root) {
Queue<TreeNode> queue = new LinkedList<>();
if (root == null) {
return;
}
queue.offer(root);
while (!queue.isEmpty()) {
TreeNode cur = queue.poll();
System.out.print(cur.val + " ");
if (cur.left != null) {
queue.offer(cur.left);
}
if (cur.right != null) {
queue.offer(cur.right);
}
}
System.out.println();
}
判断一棵树是不是完全二叉树
java复制代码
boolean isCompleteTree(TreeNode root) {
Queue<TreeNode> queue = new LinkedList<>();
if (root == null) return true;
queue.offer(root);
while (!queue.isEmpty()) {
TreeNode cur = queue.poll();
if (cur == null) {
break;
}
queue.offer(cur.left);
queue.offer(cur.right);
}
while (!queue.isEmpty()) {
TreeNode node = queue.peek();
if (node != null) {
return false;
} else {
queue.poll();
}
}
return true;
}
