CodingQuestion/src/LeetCode-199-Binary-Tree-Right-Side-View.java at master · drinkbeer/CodingQuestion · GitHub

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/*
LeetCode: https://leetcode.com/problems/binary-tree-right-side-view/
LintCode:
JiuZhang:
ProgramCreek: http://www.programcreek.com/2014/04/leetcode-binary-tree-right-side-view-java/

Analysis:
1.BFS(Two queues)

2.BFS(One queue)

3.DFS
HashMap.put(key, value), if the key is existed, the latter value will overwritten the former one
*/
/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode(int x) { val = x; }
 * }
 */
public class Solution {
    // 1.BFS(Two queues)
    // public List<Integer> rightSideView(TreeNode root) {
    //     List<Integer> result = new ArrayList<Integer>();
    //     if(root == null) return result;

    //     Queue<TreeNode> currLevel = new LinkedList<TreeNode>();
    //     currLevel.offer(root);

    //     while(!currLevel.isEmpty()){
    //         Queue<TreeNode> nextLevel = new LinkedList<TreeNode>();
    //         int len = currLevel.size();
    //         result.add(currLevel.peek().val);

    //         for(int i = 0; i < len; i++){
    //             TreeNode curr = currLevel.poll();
    //             if(curr.right != null) nextLevel.offer(curr.right);
    //             if(curr.left != null) nextLevel.offer(curr.left);
    //         }
    //         currLevel = nextLevel;
    //     }

    //     return result;
    // }

    // 2.BFS(One queue)
    // public List<Integer> rightSideView(TreeNode root) {
    //     List<Integer> result = new ArrayList<Integer>();
    //     if(root == null) return result;

    //     Queue<TreeNode> queue = new LinkedList<TreeNode>();
    //     queue.offer(root);

    //     while(!queue.isEmpty()){
    //         int len = queue.size();
    //         result.add(queue.peek().val);

    //         for(int i = 0; i < len; i++){
    //             TreeNode curr = queue.poll();
    //             if(curr.right != null) queue.offer(curr.right);
    //             if(curr.left != null) queue.offer(curr.left);
    //         }
    //     }
    //     return result;
    // }

    // 1.BFS (level order traversal, using a Queue)
//     public List<Integer> rightSideView(TreeNode root) {
//         List<Integer> result = new ArrayList<Integer>();
//         if (root == null) return result;

//         Queue<TreeNode> queue = new LinkedList<>();
//         queue.add(root);

//         while(!queue.isEmpty()) {
//             int size = queue.size();
//             TreeNode curr = null;
//             for (int i = 0; i < size; i++) {
//                 curr = queue.poll();
//                 if (curr.left != null) queue.add(curr.left);
//                 if (curr.right != null) queue.add(curr.right);
//             }
//             result.add(curr.val);
//         }

//         return result;
//     }

    // 3.DFS
    public List<Integer> rightSideView(TreeNode root) {
        List<Integer> result = new ArrayList<Integer>();
        if(root == null) return result;

        HashMap<Integer, Integer> depthToValue = new HashMap<Integer, Integer>();
        DFS(depthToValue, root, 1);

        int depth = 1;
        while(depthToValue.containsKey(depth)){
            result.add(depthToValue.get(depth));
            depth++;
        }
        return result;
    }

    private void DFS(HashMap<Integer, Integer> depthToValue, TreeNode root, int depth){
        if(root == null) return;

        depthToValue.put(depth, root.val);
        if(root.left != null) DFS(depthToValue, root.left, depth + 1);
        if(root.right != null) DFS(depthToValue, root.right, depth + 1);
    }


    // 1.BFS. Both left size view and right side view.
    //     public List<Integer> rightSideView(TreeNode root) {
//         if (root == null) return new ArrayList<>();

//         List<Integer> left = new ArrayList<>();
//         List<Integer> right = new ArrayList<>();

//         Queue<TreeNode> queue = new LinkedList<>();
//         queue.add(root);

//         while(!queue.isEmpty()) {
//             int size = queue.size();

//             for(int i = 0; i < size; i++) {
//                 TreeNode curr = queue.poll();

//                 if (i == 0) left.add(curr.val);
//                 if (i == size - 1) right.add(curr.val);

//                 if (curr.left != null) queue.add(curr.left);
//                 if (curr.right != null) queue.add(curr.right);
//             }
//         }

//         return right;

//     }

    // 2.BFS Recursion. Both left size view and right side view.
    public List<Integer> rightSideView(TreeNode root) {
        if (root == null) return new ArrayList<>();

        List<Integer> left = new ArrayList<>();
        List<Integer> right = new ArrayList<>();

        helper(root, 0, left, right);

        System.out.println(left.toString());
        System.out.println(right.toString());
        return right;
    }

    private void helper(TreeNode root, int level, List<Integer> left, List<Integer> right) {
        if (left.size() <= level) left.add(level, root.val);
        if (right.size() <= level) {
            right.add(level, root.val);
        } else {
            right.set(level, root.val);
        }

        if (root.left != null) helper(root.left, level + 1, left, right);
        if (root.right != null) helper(root.right, level + 1, left, right);
    }

}