Binary Tree

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import java.util.LinkedList;
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import java.util.Queue;
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public int fn(TreeNode root) {
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    Queue<TreeNode> que = new LinkedList<>();
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    que.add(root);
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    int ans = 0;
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    while (!que.isEmpty()) {
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        int currentLength = que.size();
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        // TODO: logic for current level
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        for (int i = 0; i < currentLength; i++) {
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            TreeNode node = que.remove();
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            // TODO: logic
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            if (node.left != null) {
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                que.add(node.left);
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            }
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            if (node.right != null) {
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                que.add(node.right);
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            }
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        }
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    }
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    return ans;
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}

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import java.util.Stack;
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public int dfs(TreeNode root) {
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    Stack<TreeNode> stack = new Stack<>();
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    stack.push(root);
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    int ans = 0;
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    while (!stack.isEmpty()) {
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        TreeNode node = stack.pop();
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        // TODO: logic
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        if (node.left != null) {
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            stack.push(node.left);
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        }
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        if (node.right != null) {
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            stack.push(node.right);
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        }
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    }
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    return ans;
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}

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public int dfs(TreeNode root) {
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    if (root == null) {
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        return 0;
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    }
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    int ans = 0;
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    // TODO: logic
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    ans += dfs(root.left);
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    ans += dfs(root.right);
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    return ans;
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}