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Level_Order.java
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60 lines (41 loc) · 1.77 KB
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package Algorithms;
import java.util.ArrayDeque;
import java.util.ArrayList;
import java.util.Queue;
public class Level_Order {
public ArrayList<ArrayList<Integer>> levelOrder(TreeNode root) {
ArrayList<ArrayList<Integer>> levelOrder = new ArrayList<ArrayList<Integer>>();
if (root == null){
return levelOrder;
}
// record the level of the tree. 0: root.
//int level = 0;
Queue<TreeNode> queue = new ArrayDeque<TreeNode>();
// add the root to the queue.
queue.add(root);
// init the 0 level of the order.
//levelOrder[level] = new ArrayList<Integer>;
// get all the elements out from the queue.
while(!queue.isEmpty()){
// get the size of this level;
int size = queue.size();
ArrayList<Integer> tmpList = new ArrayList<Integer>();
levelOrder.add(tmpList);
// add this level to the array and store all the elements in the next level.
for(int i = 0; i < size; i++){
TreeNode currElement = queue.remove();
// add all the element in this level to the arraylist.
tmpList.add(currElement.val);
// add all the element in the next level to the queue.
if(currElement.left != null){
queue.add(currElement.left);
}
if(currElement.right != null){
queue.add(currElement.right);
}
}
//level ++;
}
return levelOrder;
}
}