ZigZagLevelOrderTraversal
ZigZagLevelOrderTraversal.java 源码
package datastructure.tree.leetcode;
import java.util.ArrayList;
import java.util.LinkedList;
import java.util.List;
import java.util.Queue;
/**
* 二叉树的锯齿形遍历
*/
public class ZigZagLevelOrderTraversal {
/**
* 广度优先搜索
*/
public List<List<Integer>> zigzagLevelOrder1(TreeNode root) {
List<List<Integer>> res = new ArrayList<>();
if (root == null) {
return res;
}
Queue<TreeNode> queue = new LinkedList<>();
queue.add(root);
int level = 0;
while (!queue.isEmpty()) {
int n = queue.size();
level++;
List<Integer> list = new ArrayList<>();
for (int i = 0; i < n; i++) {
TreeNode node = queue.poll();
if (level % 2 == 0) {
list.add(0, node.val);
} else {
list.add(node.val);
}
if (node.left != null) {
queue.add(node.left);
}
if (node.right != null) {
queue.add(node.right);
}
}
res.add(list);
}
return res;
}
/**
* 再来用深度优先搜索搞一搞
*/
public List<List<Integer>> zigzagLevelOrder2(TreeNode root) {
List<List<Integer>> res = new ArrayList<>();
dfs(root, 0, res);
return res;
}
private void dfs(TreeNode root, int level, List<List<Integer>> res) {
if (root == null) {
return;
}
if (level == res.size()) {
res.add(new ArrayList<>());
}
if (level % 2 == 0) {
res.get(level).add(root.val);
} else {
res.get(level).add(0, root.val);
}
dfs(root.left, level + 1, res);
dfs(root.right, level + 1, res);
}
public static class TreeNode {
int val;
TreeNode left;
TreeNode right;
TreeNode(int x) { val = x; }
}
}
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