LC.P655[输出二叉树]

方法一：DFS

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/**
 * Definition for a binary tree node.
 * public class TreeNode {
 *     int val;
 *     TreeNode left;
 *     TreeNode right;
 *     TreeNode() {}
 *     TreeNode(int val) { this.val = val; }
 *     TreeNode(int val, TreeNode left, TreeNode right) {
 *         this.val = val;
 *         this.left = left;
 *         this.right = right;
 *     }
 * }
 */
class Solution {
    List<List<String>> ans;
    int height;

    public List<List<String>> printTree(TreeNode root) {
        getHeight(root, 0);
        int m = height + 1, n = (1 << height + 1) - 1;
        ans = new ArrayList<>();
        for (int i = 0; i < m; ++i) {
            List<String> list = new ArrayList<>();
            for (int j = 0; j < n; ++j) {
                list.add("");
            }
            ans.add(list);
        }
        dfs(root, 0, (n - 1) >> 1);
        return ans;
    }

    private void dfs(TreeNode root, int r, int c) {
        if (root == null) return;
        ans.get(r).set(c, String.valueOf(root.val));
        dfs(root.left, r + 1, c - (1 << height - r - 1));
        dfs(root.right, r + 1, c + (1 << height - r - 1));
    }

    private void getHeight(TreeNode root, int depth) {
        if (root == null) return;
        height = Math.max(height, depth);
        getHeight(root.left, depth + 1);
        getHeight(root.right, depth + 1);
    }
}
  • 时间复杂度：$O(nm)$
  • 空间复杂度：$O(nm)$