class036 二叉树高频题目-上-不含树型dp【算法】-编程知识

class036 二叉树高频题目-上-不含树型dp

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code1 102. 二叉树的层序遍历

// 二叉树的层序遍历
// 测试链接 : https://leetcode.cn/problems/binary-tree-level-order-traversal/

code1 普通bfs
code2 一次操作一层

package class036;import java.util.ArrayList;
import java.util.HashMap;
import java.util.LinkedList;
import java.util.List;
import java.util.Queue;// 二叉树的层序遍历
// 测试链接 : https://leetcode.cn/problems/binary-tree-level-order-traversal/
public class Code01_LevelOrderTraversal {// 不提交这个类public static class TreeNode {public int val;public TreeNode left;public TreeNode right;}// 提交时把方法名改为levelOrder，此方法为普通bfs，此题不推荐public static List<List<Integer>> levelOrder1(TreeNode root) {List<List<Integer>> ans = new ArrayList<>();if (root != null) {Queue<TreeNode> queue = new LinkedList<>();HashMap<TreeNode, Integer> levels = new HashMap<>();queue.add(root);levels.put(root, 0);while (!queue.isEmpty()) {TreeNode cur = queue.poll();int level = levels.get(cur);if (ans.size() == level) {ans.add(new ArrayList<>());}ans.get(level).add(cur.val);if (cur.left != null) {queue.add(cur.left);levels.put(cur.left, level + 1);}if (cur.right != null) {queue.add(cur.right);levels.put(cur.right, level + 1);}}}return ans;}// 如果测试数据量变大了就修改这个值public static int MAXN = 2001;public static TreeNode[] queue = new TreeNode[MAXN];public static int l, r;// 提交时把方法名改为levelOrder，此方法为每次处理一层的优化bfs，此题推荐public static List<List<Integer>> levelOrder2(TreeNode root) {List<List<Integer>> ans = new ArrayList<>();if (root != null) {l = r = 0;queue[r++] = root;while (l < r) { // 队列里还有东西int size = r - l;ArrayList<Integer> list = new ArrayList<Integer>();for (int i = 0; i < size; i++) {TreeNode cur = queue[l++];list.add(cur.val);if (cur.left != null) {queue[r++] = cur.left;}if (cur.right != null) {queue[r++] = cur.right;}}ans.add(list);}}return ans;}}

code2 103. 二叉树的锯齿形层序遍历

// 二叉树的锯齿形层序遍历
// 测试链接 : https://leetcode.cn/problems/binary-tree-zigzag-level-order-traversal/

code 遍历

package class036;import java.util.ArrayList;
import java.util.List;// 二叉树的锯齿形层序遍历
// 测试链接 : https://leetcode.cn/problems/binary-tree-zigzag-level-order-traversal/
public class Code02_ZigzagLevelOrderTraversal {// 不提交这个类public static class TreeNode {public int val;public TreeNode left;public TreeNode right;}// 提交以下的方法// 用每次处理一层的优化bfs就非常容易实现// 如果测试数据量变大了就修改这个值public static int MAXN = 2001;public static TreeNode[] queue = new TreeNode[MAXN];public static int l, r;public static List<List<Integer>> zigzagLevelOrder(TreeNode root) {List<List<Integer>> ans = new ArrayList<>();if (root != null) {l = r = 0;queue[r++] = root;// false 代表从左往右// true 代表从右往左boolean reverse = false; while (l < r) {int size = r - l;ArrayList<Integer> list = new ArrayList<Integer>();// reverse == false, 左 -> 右， l....r-1, 收集size个// reverse == true,  右 -> 左， r-1....l, 收集size个// 左 -> 右, i = i + 1// 右 -> 左, i = i - 1for (int i = reverse ? r - 1 : l, j = reverse ? -1 : 1, k = 0; k < size; i += j, k++) {TreeNode cur = queue[i];list.add(cur.val);}for (int i = 0; i < size; i++) {TreeNode cur = queue[l++];if (cur.left != null) {queue[r++] = cur.left;}if (cur.right != null) {queue[r++] = cur.right;}}ans.add(list);reverse = !reverse;}}return ans;}}

code3 662. 二叉树最大宽度

// 二叉树的最大特殊宽度
// 测试链接 : https://leetcode.cn/problems/maximum-width-of-binary-tree/

package class036;// 二叉树的最大特殊宽度
// 测试链接 : https://leetcode.cn/problems/maximum-width-of-binary-tree/
public class Code03_WidthOfBinaryTree {// 不提交这个类public static class TreeNode {public int val;public TreeNode left;public TreeNode right;}// 提交以下的方法// 用每次处理一层的优化bfs就非常容易实现// 如果测试数据量变大了就修改这个值public static int MAXN = 3001;public static TreeNode[] nq = new TreeNode[MAXN];public static int[] iq = new int[MAXN];public static int l, r;public static int widthOfBinaryTree(TreeNode root) {int ans = 1;l = r = 0;nq[r] = root;iq[r++] = 1;while (l < r) {int size = r - l;ans = Math.max(ans, iq[r - 1] - iq[l] + 1);for (int i = 0; i < size; i++) {TreeNode node = nq[l];int id = iq[l++];if (node.left != null) {nq[r] = node.left;iq[r++] = id * 2;}if (node.right != null) {nq[r] = node.right;iq[r++] = id * 2 + 1;}}}return ans;}}

code4 104. 二叉树的最大深度 111. 二叉树的最小深度

// 求二叉树的最大、最小深度
// 测试链接 : https://leetcode.cn/problems/maximum-depth-of-binary-tree/
// 测试链接 : https://leetcode.cn/problems/minimum-depth-of-binary-tree/

package class036;// 求二叉树的最大、最小深度
public class Code04_DepthOfBinaryTree {// 不提交这个类public static class TreeNode {public int val;public TreeNode left;public TreeNode right;}// 测试链接 : https://leetcode.cn/problems/maximum-depth-of-binary-tree/public static int maxDepth(TreeNode root) {return root == null ? 0 : Math.max(maxDepth(root.left), maxDepth(root.right)) + 1;}// 测试链接 : https://leetcode.cn/problems/minimum-depth-of-binary-tree/public int minDepth(TreeNode root) {if (root == null) {// 当前的树是空树return 0;}if (root.left == null && root.right == null) {// 当前root是叶节点return 1;}int ldeep = Integer.MAX_VALUE;int rdeep = Integer.MAX_VALUE;if (root.left != null) {ldeep = minDepth(root.left);}if (root.right != null) {rdeep = minDepth(root.right);}return Math.min(ldeep, rdeep) + 1;}}

code5 297. 二叉树的序列化与反序列化

// 二叉树先序序列化和反序列化
// 测试链接 : https://leetcode.cn/problems/serialize-and-deserialize-binary-tree/

package class036;// 二叉树先序序列化和反序列化
// 测试链接 : https://leetcode.cn/problems/serialize-and-deserialize-binary-tree/
public class Code05_PreorderSerializeAndDeserialize {// 不提交这个类public static class TreeNode {public int val;public TreeNode left;public TreeNode right;public TreeNode(int v) {val = v;}}// 二叉树可以通过先序、后序或者按层遍历的方式序列化和反序列化// 但是，二叉树无法通过中序遍历的方式实现序列化和反序列化// 因为不同的两棵树，可能得到同样的中序序列，即便补了空位置也可能一样。// 比如如下两棵树//         __2//        ///       1//       和//       1__//          \//           2// 补足空位置的中序遍历结果都是{ null, 1, null, 2, null}// 提交这个类public class Codec {public String serialize(TreeNode root) {StringBuilder builder = new StringBuilder();f(root, builder);return builder.toString();}void f(TreeNode root, StringBuilder builder) {if (root == null) {builder.append("#,");} else {builder.append(root.val + ",");f(root.left, builder);f(root.right, builder);}}public TreeNode deserialize(String data) {String[] vals = data.split(",");cnt = 0;return g(vals);}// 当前数组消费到哪了public static int cnt;TreeNode g(String[] vals) {String cur = vals[cnt++];if (cur.equals("#")) {return null;} else {TreeNode head = new TreeNode(Integer.valueOf(cur));head.left = g(vals);head.right = g(vals);return head;}}}}

code6 105. 从前序与中序遍历序列构造二叉树

// 利用先序与中序遍历序列构造二叉树
// 测试链接 : https://leetcode.cn/problems/construct-binary-tree-from-preorder-and-inorder-traversal/

package class036;// 二叉树按层序列化和反序列化
// 测试链接 : https://leetcode.cn/problems/serialize-and-deserialize-binary-tree/
public class Code06_LevelorderSerializeAndDeserialize {// 不提交这个类public static class TreeNode {public int val;public TreeNode left;public TreeNode right;public TreeNode(int v) {val = v;}}// 提交这个类// 按层序列化public class Codec {public static int MAXN = 10001;public static TreeNode[] queue = new TreeNode[MAXN];public static int l, r;public String serialize(TreeNode root) {StringBuilder builder = new StringBuilder();if (root != null) {builder.append(root.val + ",");l = 0;r = 0;queue[r++] = root;while (l < r) {root = queue[l++];if (root.left != null) {builder.append(root.left.val + ",");queue[r++] = root.left;} else {builder.append("#,");}if (root.right != null) {builder.append(root.right.val + ",");queue[r++] = root.right;} else {builder.append("#,");}}}return builder.toString();}public TreeNode deserialize(String data) {if (data.equals("")) {return null;}String[] nodes = data.split(",");int index = 0;TreeNode root = generate(nodes[index++]);l = 0;r = 0;queue[r++] = root;while (l < r) {TreeNode cur = queue[l++];cur.left = generate(nodes[index++]);cur.right = generate(nodes[index++]);if (cur.left != null) {queue[r++] = cur.left;}if (cur.right != null) {queue[r++] = cur.right;}}return root;}private TreeNode generate(String val) {return val.equals("#") ? null : new TreeNode(Integer.valueOf(val));}}}

code7 958. 二叉树的完全性检验

// 验证完全二叉树
// 测试链接 : https://leetcode.cn/problems/check-completeness-of-a-binary-tree/

1)无左有右 flase
2)孩子不全开始必须都是叶子结点，否则false

package class036;import java.util.HashMap;// 利用先序与中序遍历序列构造二叉树
// 测试链接 : https://leetcode.cn/problems/construct-binary-tree-from-preorder-and-inorder-traversal/
public class Code07_PreorderInorderBuildBinaryTree {// 不提交这个类public static class TreeNode {public int val;public TreeNode left;public TreeNode right;public TreeNode(int v) {val = v;}}// 提交如下的方法public static TreeNode buildTree(int[] pre, int[] in) {if (pre == null || in == null || pre.length != in.length) {return null;}HashMap<Integer, Integer> map = new HashMap<>();for (int i = 0; i < in.length; i++) {map.put(in[i], i);}return f(pre, 0, pre.length - 1, in, 0, in.length - 1, map);}public static TreeNode f(int[] pre, int l1, int r1, int[] in, int l2, int r2, HashMap<Integer, Integer> map) {if (l1 > r1) {return null;}TreeNode head = new TreeNode(pre[l1]);if (l1 == r1) {return head;}int k = map.get(pre[l1]);// pre : l1(........)[.......r1]// in  : (l2......)k[........r2]// (...)是左树对应，[...]是右树的对应head.left = f(pre, l1 + 1, l1 + k - l2, in, l2, k - 1, map);head.right = f(pre, l1 + k - l2 + 1, r1, in, k + 1, r2, map);return head;}}

code8 222. 完全二叉树的节点个数

// 求完全二叉树的节点个数
// 测试链接 : https://leetcode.cn/problems/count-complete-tree-nodes/

package class036;// 验证完全二叉树
// 测试链接 : https://leetcode.cn/problems/check-completeness-of-a-binary-tree/
public class Code08_CompletenessOfBinaryTree {// 不提交这个类public static class TreeNode {public int val;public TreeNode left;public TreeNode right;}// 提交以下的方法// 如果测试数据量变大了就修改这个值public static int MAXN = 101;public static TreeNode[] queue = new TreeNode[MAXN];public static int l, r;public static boolean isCompleteTree(TreeNode h) {if (h == null) {return true;}l = r = 0;queue[r++] = h;// 是否遇到过左右两个孩子不双全的节点boolean leaf = false;while (l < r) {h = queue[l++];if ((h.left == null && h.right != null) || (leaf && (h.left != null || h.right != null))) {return false;}if (h.left != null) {queue[r++] = h.left;}if (h.right != null) {queue[r++] = h.right;}if (h.left == null || h.right == null) {leaf = true;}}return true;}}

code9 222. 完全二叉树的节点个数

// 求完全二叉树的节点个数
// 测试链接 : https://leetcode.cn/problems/count-complete-tree-nodes/

package class036;// 求完全二叉树的节点个数
// 测试链接 : https://leetcode.cn/problems/count-complete-tree-nodes/
public class Code09_CountCompleteTreeNodes {// 不提交这个类public static class TreeNode {public int val;public TreeNode left;public TreeNode right;}// 提交如下的方法public static int countNodes(TreeNode head) {if (head == null) {return 0;}return f(head, 1, mostLeft(head, 1));}// cur : 当前来到的节点// level :  当前来到的节点在第几层// h : 整棵树的高度，不是cur这棵子树的高度// 求 : cur这棵子树上有多少节点public static int f(TreeNode cur, int level, int h) {if (level == h) {return 1;}if (mostLeft(cur.right, level + 1) == h) {// cur右树上的最左节点，扎到了最深层return (1 << (h - level)) + f(cur.right, level + 1, h);} else {// cur右树上的最左节点，没扎到最深层return (1 << (h - level - 1)) + f(cur.left, level + 1, h);}}// 当前节点是cur，并且它在level层// 返回从cur开始不停往左，能扎到几层public static int mostLeft(TreeNode cur, int level) {while (cur != null) {level++;cur = cur.left;}return level - 1;}}