LeetCode二叉树知识大纲

ADT

    public static class TreeNode {
        int val;

        TreeNode left;

        TreeNode right;

        TreeNode(int val, TreeNode left, TreeNode right) {
            this.val = val;
            this.left = left;
            this.right = right;
        }
    }

构建二叉树

    public static void main(String[] args) {
        TreeNode node4 = new TreeNode(4);
        TreeNode node2 = new TreeNode(2);
        TreeNode node6 = new TreeNode(6);
        TreeNode node5 = new TreeNode(5);
        TreeNode node3 = new TreeNode(3);
        TreeNode node1 = new TreeNode(1);

        node2.left = node3;
        node2.right = node4;

        node1.left = node2;
        node1.right = node5;

        node5.right = node6;

        TreeDfs dfs = new TreeDfs();
        dfs.bfs(node1);
    }

深度优先搜索遍历

    public void dfs(TreeNode root) {
        if (root == null) {
            return;
        }
        System.out.print(root.val);

        dfs(root.left);
        dfs(root.right);
    }

广度优先搜索遍历

    public void bfs(TreeNode node) {
        ArrayDeque<TreeNode> q = new ArrayDeque();
        q.add(node);

        while (q.size() > 0) {
            TreeNode node1 = q.pop();
            System.out.print(node1.val);

            if (node1.left != null) {
                q.add(node1.left);
            }
            if (node1.right != null) {
                q.add(node1.right);
            }
        }
    }

使用bfs记录树层级

        添加map记录node与层数。

    public void bfsWithLevel(TreeNode node) {
        ArrayDeque<TreeNode> q = new ArrayDeque();
        Map<TreeNode, Integer> tmp = new HashMap<>();
        tmp.put(node, 0);
        q.add(node);

        while (q.size() > 0) {
            TreeNode node1 = q.pop();
            System.out.println(node1.val + " >>>> " + tmp.get(node1));

            if (node1.left != null) {
                q.add(node1.left);
                tmp.put(node1.left, tmp.get(node1) + 1);
            }
            if (node1.right != null) {
                q.add(node1.right);
                tmp.put(node1.right, tmp.get(node1) + 1);
            }
        }
    }