_199.java

package com.fishercoder.solutions.firstthousand;

import com.fishercoder.common.classes.TreeNode;
import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;
import java.util.Queue;

public class _199 {

    public static class Solution1 {
        /*
         * credit: https://leetcode.com/problems/binary-tree-right-side-view/discuss/56012/My-simple-accepted-solution(JAVA)
         */
        public List<Integer> rightSideView(TreeNode root) {
            List<Integer> result = new ArrayList<>();
            rightView(root, result, 0);
            return result;
        }

        void rightView(TreeNode curr, List<Integer> result, int currDepth) {
            if (curr == null) {
                return;
            }
            if (currDepth == result.size()) {
                result.add(curr.val);
            }
            // go through right side first as we want right side view, so as soon as we find it,
            // then we won't use the one from left side
            rightView(curr.right, result, currDepth + 1);
            rightView(curr.left, result, currDepth + 1);
        }
    }

    public static class Solution2 {
        /*
         * BFS the tree
         */
        public List<Integer> rightSideView(TreeNode root) {
            List<Integer> result = new ArrayList<>();
            if (root == null) {
                return result;
            }
            Queue<TreeNode> q = new LinkedList<>();
            q.offer(root);
            while (!q.isEmpty()) {
                int size = q.size();
                for (int i = 0; i < size; i++) {
                    TreeNode curr = q.poll();
                    if (i == size - 1) {
                        result.add(curr.val);
                    }
                    if (curr.left != null) {
                        q.offer(curr.left);
                    }
                    if (curr.right != null) {
                        q.offer(curr.right);
                    }
                }
            }
            return result;
        }
    }
}