LeetCode39|找树左下角的值

输入:

    2
   / \
  1   3

输出:
1


输入:

        1
       / \
      2   3
     /   / \
    4   5   6
       /
      7

输出:
7
注意: 您可以假设树（即给定的根节点）不为 NULL。

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

public class FindBottomLeftValueTest {
    public static void main(String[] args) {
        TreeNode t1 = new TreeNode(2);
        TreeNode t2 = new TreeNode(1);
        TreeNode t3 = new TreeNode(3);
        t1.left = t2;
        t1.right = t3;
        int bottomLeftValue = findBottomLeftValue(t1);
        System.out.println("bottomLeftValue = " + bottomLeftValue);

        int leftValue = findBottomLeftValue2(t1);
        System.out.println("leftValue = " + leftValue);
    }

    public static int findBottomLeftValue(TreeNode root) {
        if (root == null) {
            return 0;
        }
        List<List<Integer>> listList = new ArrayList<>();
        Queue<TreeNode> queue = new LinkedList<>();
        queue.add(root);
        while (!queue.isEmpty()) {
            int size = queue.size();
            List<Integer> list = new ArrayList<>();
            for (int i = 0; i < size; i++) {
                TreeNode node = queue.poll();
                list.add(node.val);
                if (node.left != null) {
                    queue.add(node.left);
                }
                if (node.right != null) {
                    queue.add(node.right);
                }
            }
            listList.add(list);
        }
        return listList.get(listList.size() - 1).get(0);
    }

    public static int findBottomLeftValue2(TreeNode root) {
        if (root == null) {
            return 0;
        }
        Queue<TreeNode> queue = new LinkedList<>();
        queue.add(root);
        int result = 0;
        while (!queue.isEmpty()) {
            int size = queue.size();
            for (int i = 0; i < size; i++) {
                TreeNode node = queue.poll();
                result = node.val;
                if (node.right != null) {
                    queue.add(node.right);
                }
                if (node.left != null) {
                    queue.add(node.left);
                }

            }
        }
        return result;
    }
}