二叉树简单题|对称、翻转、合并二叉树

模板代码

private boolean process(TreeNode p, TreeNode q) {
    if (p == null && q == null) {
    	return ;
    } else if (p == null && q != null) {
    	return ;
    } else if (p != null && q == null) {
    	return ;
    } else {
    	return ;
    }
}

101 对称二叉树

/**
 * 对称二叉树
 */
public class $101 {
    public boolean isSymmetric(TreeNode root) {
        if (root == null) {
            return false;
        }
        return process(root.left, root.right);
    }

    private boolean process(TreeNode p, TreeNode q) {
        if (p == null && q == null) {
            return true;
        } else if (p == null && q != null) {
            return false;
        } else if (p != null && q == null) {
            return false;
        } else {
            return p.val == q.val && process(p.left, q.right) && process(p.right, q.left);
        }
    }
}

226 翻转二叉树

import java.util.LinkedList;
import java.util.List;

/**
 * 翻转二叉树
 */
public class $226 {
    public TreeNode invertTree(TreeNode root) {
        if (root == null) {
            return null;
        }

        return process(root);
    }

    private TreeNode process(TreeNode root) {
        if (root.left == null && root.right == null) {
            return root;
        } else if (root.left == null && root.right != null) {
            TreeNode rigRes = process(root.right);
            root.left = rigRes;
            root.right = null;
            return root;
        } else if (root.left != null && root.right == null) {
            TreeNode lefRes = process(root.left);
            root.right = lefRes;
            root.left = null;
            return root;
        } else {
            TreeNode lefRes = process(root.left);
            TreeNode rigRes = process(root.right);
            root.left = rigRes;
            root.right = lefRes;
            return root;
        }
    }
}

617 合并二叉树

/**
 * 合并二叉树
 */
public class $617 {
    public TreeNode mergeTrees(TreeNode root1, TreeNode root2) {
        return process(root1, root2);
    }

    private TreeNode process(TreeNode p, TreeNode q) {
        if (p == null && q == null) {
            return null;
        } else if (p == null && q != null) {
            return q;
        } else if (p != null && q == null) {
            return p;
        } else {
            TreeNode node = new TreeNode(p.val + q.val);
            node.left = process(p.left, q.left);
            node.right = process(p.right, q.right);
            return node;
        }
    }
}