leetcode — same-tree

import java.util.Stack;

/**
 * Source : https://oj.leetcode.com/problems/same-tree/
 *
 *
 * Given two binary trees, write a function to check if they are equal or not.
 *
 * Two binary trees are considered equal if they are structurally identical and the nodes have the same value.
 */
public class SameTree {

    /**
     * 比较两个是否相同
     * 如果两棵树都为空，相同
     * 如果只有一棵树为空，不相同
     * 如果两棵树都不为空，则根节点相同，递归判断左右节点也要相同
     *
     * @param tree1
     * @param tree2
     * @return
     */
    public boolean isSame (TreeNode tree1, TreeNode tree2) {
        if (tree1 == null && tree2 == null) {
            return true;
        }
        if ((tree1 == null && tree2 != null) || (tree1 != null && tree2 == null)) {
            return false;
        }
        if (tree1.value != tree2.value) {
            return false;
        }
        return isSame(tree1.leftChild, tree2.leftChild) && isSame(tree1.rightChild, tree2.rightChild);
    }

    /**
     * 不使用递归，使用循环判断
     *
     * @param tree1
     * @param tree2
     * @return
     */
    public boolean isSameByIterator (TreeNode tree1, TreeNode tree2) {
        Stack<TreeNode> stack1 = new Stack<TreeNode>();
        Stack<TreeNode> stack2 = new Stack<TreeNode>();
        stack1.push(tree1);
        stack2.push(tree2);

        while (stack1.size() > 0 && stack2.size() > 0) {
            TreeNode node1 = stack1.pop();
            TreeNode node2 = stack2.pop();
            if (node1 == null && node2 == null) {
                continue;
            }
            if ((node1 == null && node2 != null) || (node1 != null && node2 == null)) {
                return false;
            }
            if (node1.value != node2.value) {
                return false;
            }
            stack1.push(node1.leftChild);
            stack1.push(node1.rightChild);
            stack2.push(node2.leftChild);
            stack2.push(node2.rightChild);
        }

        return true;

    }

    public TreeNode createTree (char[] treeArr) {
        TreeNode[] tree = new TreeNode[treeArr.length];
        for (int i = 0; i < treeArr.length; i++) {
            if (treeArr[i] == '#') {
                tree[i] = null;
                continue;
            }
            tree[i] = new TreeNode(treeArr[i]-'0');
        }
        int pos = 0;
        for (int i = 0; i < treeArr.length && pos < treeArr.length-1; i++) {
            if (tree[i] != null) {
                tree[i].leftChild = tree[++pos];
                if (pos < treeArr.length-1) {
                    tree[i].rightChild = tree[++pos];
                }
            }
        }
        return tree[0];
    }

    private class TreeNode {
        TreeNode leftChild;
        TreeNode rightChild;
        int value;

        public TreeNode(int value) {
            this.value = value;
        }

        public TreeNode() {
        }
    }

    public static void main(String[] args) {
        SameTree sameTree = new SameTree();
        char[] tree1 = new char[]{'1','2','3','#','#','4'};
        char[] tree2 = new char[]{'1','2','3','#','#','4'};
        char[] tree3 = new char[]{'1','2','3','2','#','4'};

        System.out.println(sameTree.isSame(sameTree.createTree(tree1), sameTree.createTree(tree2)) + "---true");
        System.out.println(sameTree.isSame(sameTree.createTree(tree1), sameTree.createTree(tree3)) + "---false");

        System.out.println(sameTree.isSameByIterator(sameTree.createTree(tree1), sameTree.createTree(tree2)) + "---true");
        System.out.println(sameTree.isSameByIterator(sameTree.createTree(tree1), sameTree.createTree(tree3)) + "---false");
    }

}