Java树的子结构(递归)

剑指offer 26. 树的子结构

class Solution {
    public boolean isSubStructure(TreeNode A, TreeNode B) {
        return (A != null && B != null) && (recur(A, B) || isSubStructure(A.left, B) || isSubStructure(A.right, B)); 
    }
    public boolean recur(TreeNode A, TreeNode B){
        if(B == null) return true;
        if(A == null || A.val != B.val) return false;
        return recur(A.left, B.left) && recur(A.right, B.right);
    }
}

剑指offer 27.二叉树的镜像

class Solution {
    public TreeNode mirrorTree(TreeNode root) {
        if(root != null){
            TreeNode tmp = root.left;
            root.left = root.right;
            root.right = tmp;
            mirrorTree(root.left);
            mirrorTree(root.right);
        }
        return root;
    }
}

剑指offer 28.对称的二叉树

class Solution {
    public boolean isSymmetric(TreeNode root) {
        return root == null ? true : recur(root.left, root.right);
    }
    public boolean recur(TreeNode L, TreeNode R){
        if(L == null && R == null){
            return true;
        }
        if(L == null || R == null || L.val != R.val){
            return false;
        }
        return recur(L.left, R.right) && recur(L.right, R.left);
    }
}