LeetCode - Easy - 872. Leaf-Similar Trees-蒲公英云

LeetCode - Easy - 872. Leaf-Similar Trees

Topic

Tree
Depth-first Search

Description

https://leetcode.com/problems/leaf-similar-trees/

Consider all the leaves of a binary tree, from left to right order, the values of those leaves form a leaf value sequence.

For example, in the given tree above, the leaf value sequence is (6, 7, 4, 9, 8).

Two binary trees are considered leaf-similar if their leaf value sequence is the same.

Return true if and only if the two given trees with head nodes root1 and root2 are leaf-similar.

Example 1:

Input: root1 = [3,5,1,6,2,9,8,null,null,7,4], root2 = [3,5,1,6,7,4,2,null,null,null,null,null,null,9,8]
Output: true

Example 2:

Input: root1 = [1], root2 = [1]
Output: true

Example 3:

Input: root1 = [1], root2 = [2]
Output: false

Example 4:

Input: root1 = [1,2], root2 = [2,2]
Output: true

Example 5:

Input: root1 = [1,2,3], root2 = [1,3,2]
Output: false

Constraints:

The number of nodes in each tree will be in the range [1, 200].
Both of the given trees will have values in the range [0, 200].

Analysis

用到方便中断的迭代版前序遍历模式。

Submission

import java.util.LinkedList;
import com.lun.util.BinaryTree.TreeNode;
public class LeafSimilarTrees { 
    public boolean leafSimilar(TreeNode root1, TreeNode root2) { 
        LinkedList<TreeNode> stack1 = new LinkedList<>(), //
                stack2 = new LinkedList<>();
        stack1.push(root1);
        stack2.push(root2);
        while(true) { 
            TreeNode leaf1 = getLeaf(stack1);
            TreeNode leaf2 = getLeaf(stack2);
            if(leaf1 == null ^ leaf2 == null) { 
                return false;
            }else if(leaf1 == null && leaf2 == null) { 
                return true;
            }else { 
                if(leaf1.val != leaf2.val)
                    return false;
            }
        }
    }
    private TreeNode getLeaf(LinkedList<TreeNode> stack) { 
        while(!stack.isEmpty()) {                 
            TreeNode node = stack.pop();
            if(node.left == null && node.right == null)
                return node;
            if(node.right != null)
                stack.push(node.right);
            if(node.left != null)
                stack.push(node.left);
        }
        return null;
    }
}

Test

import static org.junit.Assert.*;
import static com.lun.util.BinaryTree.integers2BinaryTree;
import org.junit.Test;
import com.lun.util.BinaryTree.TreeNode;
public class LeafSimilarTreesTest { 
    @Test
    public void test() { 
        LeafSimilarTrees obj = new LeafSimilarTrees();
        TreeNode root1 = integers2BinaryTree(3,5,1,6,2,9,8,null,null,7,4);
        TreeNode root2 = integers2BinaryTree(3,5,1,6,7,4,2,null,null,null,null,null,null,9,8);
        assertTrue(obj.leafSimilar(root1, root2));
        assertTrue(obj.leafSimilar(integers2BinaryTree(1), integers2BinaryTree(1)));
        assertFalse(obj.leafSimilar(integers2BinaryTree(1), integers2BinaryTree(2)));
        assertTrue(obj.leafSimilar(integers2BinaryTree(1, 2), integers2BinaryTree(2, 2)));
        assertFalse(obj.leafSimilar(integers2BinaryTree(1, 2, 3), integers2BinaryTree(1,3,2)));
        assertFalse(obj.leafSimilar(integers2BinaryTree(3,5,1,6,7,4,2,null,null,null,null,null,null,9,11,null,null,8,10),// 
                        integers2BinaryTree(3,5,1,6,2,9,8,null,null,7,4)));
    }
}