對稱二叉樹（力扣）圖解、思路與實現

給定一個二叉樹，檢查它是否是映象對稱的。

/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
class Solution {
    public boolean isSymmetric(TreeNode root) {
        if(root == null) {
            return true;
        }
        return isSymmetricChild(root.left,root.right);//呼叫isSymmetricChild傳入(root.left,root.right  相當於把root.left,root.right分別給引用leftTree  rightTree
        
    }
    public boolean isSymmetricChild(TreeNode leftTree,TreeNode rightTree) {//左樹和右樹  判斷當前左樹和右樹 
        if((leftTree != null && rightTree == null) || (leftTree == null) && rightTree != null) {//結構不同
            return false;
        }
        if(leftTree == null && rightTree == null) {//只有一個節點 左右都為空
            return true;
        }
        //判斷值是否相同
              //值相同時 遞迴判斷左樹的左、右樹的右是否對稱  接下來判斷左樹的右、右樹的左是否對稱
        return (leftTree.val == rightTree.val) 
        && isSymmetricChild(leftTree.left,rightTree.right) 
        && isSymmetricChild(leftTree.right,rightTree.left);
    }
}