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BinaryTreeLevelOrderTraversalII.java

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import java.util.ArrayList;

import java.util.Collections;

import shared.TreeNode;

public class BinaryTreeLevelOrderTraversalII {

public ArrayList<ArrayList<Integer>> levelOrderBottom(TreeNode root) {

ArrayList<ArrayList<Integer>> result = new ArrayList<ArrayList<Integer>>();

if(root == null)

return result;

ArrayList<TreeNode> current = new ArrayList<TreeNode>();

ArrayList<TreeNode> next = new ArrayList<TreeNode>();

current.add(root);

while(!current.isEmpty()){

ArrayList<Integer> level = new ArrayList<Integer>();

for(int i = 0;i<current.size();i++){

if(current.get(i).left!=null)

next.add(current.get(i).left);

if(current.get(i).right !=null)

next.add(current.get(i).right);

level.add(current.get(i).val);

}

result.add(level);

ArrayList<TreeNode> temp = current;

current = next;

next = temp;

next.clear();

}

Collections.reverse(result);

return result;

}

public static void main(String[] args) {

// TODO Auto-generated method stub

}

}