LeetCode44|在每个树行中找最大值

输入:

          1
         / 
        3   2
       /      
      5   3   9

输出: [1, 3, 9]

 
import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;
import java.util.Queue;

public class LargestValuesTest {
    public static void main(String[] args) {
        TreeNode t1 = new TreeNode(1);
        TreeNode t2 = new TreeNode(3);
        TreeNode t3 = new TreeNode(2);
        TreeNode t4 = new TreeNode(5);
        TreeNode t5 = new TreeNode(3);
        TreeNode t6 = new TreeNode(9);
        t1.left = t2;
        t1.right = t3;
        t2.left = t4;
        t2.right = t5;
        t3.right = t6;
        List<Integer> integerList = largestValues(t1);
        System.out.println("integerList = " + integerList);

    }

    public static List<Integer> largestValues(TreeNode root) {
        List<Integer> list = new ArrayList<>();
        if (root == null) {
            return list;
        }
        Queue<TreeNode> queue = new LinkedList<>();
        queue.add(root);
        while (!queue.isEmpty()) {
            int size = queue.size();
            int currentLevelMaxValue = Integer.MIN_VALUE;
            for (int i = 0; i < size; i++) {
                TreeNode node = queue.poll();
                currentLevelMaxValue = Math.max(currentLevelMaxValue, node.val);
                if (node.left != null) {
                    queue.add(node.left);
                }
                if (node.right != null) {
                    queue.add(node.right);
                }
            }
            list.add(currentLevelMaxValue);
        }
        return list;
    }
}