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[剑指offer] 树[上]篇

时间:2023-09-21 22:46:39浏览次数:31  
标签:right return offer int null root public

JZ55 二叉树的深度

 1 /* 递归 */
 2 public class JZ55_1
 3 {
 4     public static int TreeDepth(TreeNode root)
 5     {
 6         if (root == null) return 0;
 7         return Math.max(TreeDepth(root.left), TreeDepth(root.right)) + 1;
 8     }
 9 }
10 
11 /* 层次遍历 */
12 public class JZ55_2
13 {
14     public static int TreeDepth(TreeNode root)
15     {
16         if (root == null) return 0;
17         Queue<TreeNode> queue = new LinkedList<>();
18         int size = -1, res = 0;
19         queue.add(root);
20         while (!queue.isEmpty())
21         {
22             size = queue.size();
23             while (size != 0)
24             {
25                 TreeNode poll = queue.poll();
26                 if (poll.left != null)
27                     queue.add(poll.left);
28                 if (poll.right != null)
29                     queue.add(poll.right);
30                 size--;
31             }
32             res++;
33         }
34         return res;
35     }
36 }

JZ77 按之字形顺序打印二叉树

 1 /* 模拟 */
 2 public class JZ77_1
 3 {
 4     public static ArrayList<ArrayList<Integer>> Print(TreeNode pRoot)
 5     {
 6         ArrayList<ArrayList<Integer>> res = new ArrayList<>();
 7         if (pRoot == null) return res;
 8         Queue<TreeNode> queue = new LinkedList<>();
 9         boolean revFlag = false;
10         queue.add(pRoot);
11         while (!queue.isEmpty())
12         {
13             ArrayList<Integer> temp = new ArrayList<>();
14             int size = queue.size();
15             while (size != 0)
16             {
17                 TreeNode poll = queue.poll();
18                 temp.add(poll.val);
19                 if (poll.left != null)
20                     queue.add(poll.left);
21                 if (poll.right != null)
22                     queue.add(poll.right);
23                 size--;
24             }
25             if (revFlag)
26                 Collections.reverse(temp);
27             res.add(temp);
28             revFlag = !revFlag;
29         }
30         return res;
31     }
32 }
33 
34 /* 双栈法 */
35 public class JZ77_2
36 {
37     public static ArrayList<ArrayList<Integer>> Print(TreeNode pRoot)
38     {
39         ArrayList<ArrayList<Integer>> res = new ArrayList<>();
40         Stack<TreeNode> stack1 = new Stack<>();
41         Stack<TreeNode> stack2 = new Stack<>();
42         if (pRoot != null)
43             stack1.push(pRoot);
44         while (!stack1.isEmpty() || !stack2.isEmpty())
45         {
46             ArrayList<Integer> temp = new ArrayList<>();
47             if (!stack1.isEmpty())
48             {
49                 while (!stack1.isEmpty())
50                 {
51                     TreeNode popNode = stack1.pop();
52                     temp.add(popNode.val);
53                     if (popNode.left != null)
54                         stack2.push(popNode.left);
55                     if (popNode.right != null)
56                         stack2.push(popNode.right);
57                 }
58             }
59             else
60             {
61                 while (!stack2.isEmpty())
62                 {
63                     TreeNode popNode = stack2.pop();
64                     temp.add(popNode.val);
65                     if (popNode.right != null)
66                         stack1.push(popNode.right);
67                     if (popNode.left != null)
68                         stack1.push(popNode.left);
69                 }
70             }
71             res.add(temp);
72         }
73         return res;
74     }
75 }

JZ54 二叉搜索树的第k个节点

 1 /* 递归 */
 2 public class JZ54_1
 3 {
 4     public static int num;
 5 
 6     public static int KthNode(TreeNode proot, int k)
 7     {
 8         num = k;
 9         return inorder(proot);
10     }
11 
12     private static int inorder(TreeNode proot)
13     {
14         if (proot != null)
15         {
16             int left = inorder(proot.left);
17             if (left != -1)
18                 return left;
19             if (num == 1)
20                 return proot.val;
21             num--;
22             return inorder(proot.right);
23         }
24         return -1;
25     }
26 }
27 
28 /* 非递归 */
29 public class JZ54_2
30 {
31     public static int KthNode(TreeNode proot, int k)
32     {
33         Stack<TreeNode> stack = new Stack<>();
34         while (!stack.isEmpty() || proot != null)
35         {
36             if (proot != null)
37             {
38                 stack.push(proot);
39                 proot = proot.left;
40             }
41             else
42             {
43                 TreeNode popNode = stack.pop();
44                 if (k == 1) return popNode.val;
45                 k--;
46                 proot = popNode.right;
47             }
48         }
49         return -1;
50     }
51 }

JZ7 重建二叉树

 1 /* 递归 */
 2 public class JZ7_1
 3 {
 4     public static TreeNode reConstructBinaryTree(int[] preOrder, int[] vinOrder)
 5     {
 6         return struct(preOrder, 0, preOrder.length - 1, vinOrder, 0, vinOrder.length - 1);
 7     }
 8 
 9     public static TreeNode struct(int[] preOrder, int preS, int preE, int[] vinOrder, int vinS, int vinE)
10     {
11         if (preS > preE || vinS > vinE) return null;
12         TreeNode root = new TreeNode(preOrder[preS]);
13         int pivot = vinS;
14         while (vinOrder[pivot] != preOrder[preS])
15             pivot++;
16         int len = pivot - vinS;
17         root.left = struct(preOrder, preS + 1, preS + len, vinOrder, vinS, pivot - 1);
18         root.right = struct(preOrder, preS + len + 1, preE, vinOrder, pivot + 1, vinE);
19         return root;
20     }
21 }

JZ26 树的子结构⭐

 1 /* 递归 */
 2 public class JZ26_1
 3 {
 4     public static boolean HasSubtree(TreeNode root1, TreeNode root2)
 5     {
 6         if (root2 == null) return false;
 7         else return fun(root1, root2);
 8     }
 9 
10     public static boolean fun(TreeNode root1, TreeNode root2)
11     {
12         if (root2 == null) return true;
13         if (root1 == null) return false;
14         boolean one = (root1.val == root2.val) && fun(root1.left, root2.left) && fun(root1.right, root2.right);
15         if (one) return true;
16         boolean two = fun(root1.left, root2) || fun(root1.right, root2);
17         return two;
18     }
19 }
20 
21 /* 递归版本2 */
22 public class JZ26_2
23 {
24     public static boolean HasSubtree(TreeNode root1, TreeNode root2)
25     {
26         boolean res = false;
27         if (root1 != null && root2 != null)
28         {
29             if (root1.val == root2.val)
30                 res = judge(root1, root2);
31             if (!res)
32                 res = HasSubtree(root1.left, root2);
33             if (!res)
34                 res = HasSubtree(root1.right, root2);
35         }
36         return res;
37     }
38 
39     public static boolean judge(TreeNode root1, TreeNode root2)
40     {
41         if (root2 == null) return true;
42         if (root1 == null) return false;
43         if (root1.val != root2.val) return false;
44         return judge(root1.left, root2.left) && judge(root1.right, root2.right);
45     }
46 }

JZ27 二叉树的镜像

 1 /* 递归 */
 2 public class JZ7_1
 3 {
 4     public static TreeNode reConstructBinaryTree(int[] preOrder, int[] vinOrder)
 5     {
 6         return struct(preOrder, 0, preOrder.length - 1, vinOrder, 0, vinOrder.length - 1);
 7     }
 8 
 9     public static TreeNode struct(int[] preOrder, int preS, int preE, int[] vinOrder, int vinS, int vinE)
10     {
11         if (preS > preE || vinS > vinE) return null;
12         TreeNode root = new TreeNode(preOrder[preS]);
13         int pivot = vinS;
14         while (vinOrder[pivot] != preOrder[preS])
15             pivot++;
16         int len = pivot - vinS;
17         root.left = struct(preOrder, preS + 1, preS + len, vinOrder, vinS, pivot - 1);
18         root.right = struct(preOrder, preS + len + 1, preE, vinOrder, pivot + 1, vinE);
19         return root;
20     }
21 }

JZ32 从上往下打印二叉树

 1 /* 层次遍历 */
 2 public class JZ32_1
 3 {
 4     public static ArrayList<Integer> PrintFromTopToBottom(TreeNode root)
 5     {
 6         ArrayList<Integer> res = new ArrayList<>();
 7         Queue<TreeNode> queue = new LinkedList<>();
 8         if (root == null) return res;
 9         queue.add(root);
10         while (!queue.isEmpty())
11         {
12             TreeNode poll = queue.poll();
13             res.add(poll.val);
14             if (poll.left != null)
15                 queue.add(poll.left);
16             if (poll.right != null)
17                 queue.add(poll.right);
18         }
19         return res;
20     }
21 }
22 
23 /* 递归 */
24 public class JZ32_2
25 {
26     public static ArrayList<Integer> PrintFromTopToBottom(TreeNode root)
27     {
28         ArrayList<ArrayList<Integer>> temp = new ArrayList<>();
29         ArrayList<Integer> res = new ArrayList<>();
30         levelTravel(root, temp, 1);
31         for (ArrayList<Integer> list : temp)
32             res.addAll(list);
33         return res;
34     }
35 
36     public static void levelTravel(TreeNode root, ArrayList<ArrayList<Integer>> temp, int depth)
37     {
38         if (root == null) return;
39         if (temp.size() < depth)
40         {
41             ArrayList<Integer> addList = new ArrayList<>();
42             addList.add(root.val);
43             temp.add(addList);
44         }
45         else
46         {
47             temp.get(depth - 1).add(root.val);
48         }
49         levelTravel(root.left, temp, depth + 1);
50         levelTravel(root.right, temp, depth + 1);
51     }
52 }

JZ33 二叉搜索树的后序遍历序列

 1 /* 递归 */
 2 public class JZ33_1
 3 {
 4     public static boolean VerifySquenceOfBST(int[] sequence)
 5     {
 6         if (sequence.length == 0) return false;
 7         return judge(sequence, 0, sequence.length - 1);
 8     }
 9 
10     public static boolean judge(int[] sequence, int left, int right)
11     {
12         if (left >= right) return true;
13         int idx = left;
14         while (sequence[idx] < sequence[right] && idx < right)
15             idx++;
16         for (int i = idx; i < right; i++)
17         {
18             if (sequence[i] < sequence[right])
19                 return false;
20         }
21         return judge(sequence, left, idx - 1) && judge(sequence, idx, right - 1);
22     }
23 }
24 
25 /* ⭐若将中序序列当作入栈序列,那么后序序列应该是合法的出栈序列⭐ */
26 public class JZ33_2
27 {
28     public static boolean VerifySquenceOfBST(int[] sequence)
29     {
30         if (sequence.length == 0) return false;
31         int j = 0;
32         ArrayList<Integer> inOrder = new ArrayList<>();
33         Stack<Integer> stack = new Stack<>();
34         for (int num : sequence) inOrder.add(num);
35         Collections.sort(inOrder);
36         for (int num : inOrder)
37         {
38             stack.add(num);
39             while (!stack.isEmpty() && stack.peek() == sequence[j])
40             {
41                 stack.pop();
42                 j++;
43             }
44         }
45         return j == sequence.length;
46     }
47 }

JZ82 二叉树中和为某一值的路径(一)

 1 /* 递归 */
 2 public class JZ82_1
 3 {
 4     public static boolean hasPathSum(TreeNode root, int sum)
 5     {
 6         if (root == null)
 7             return false;
 8         if (root.left == null && root.right == null && sum - root.val == 0)
 9             return true;
10         return hasPathSum(root.left, sum - root.val) || hasPathSum(root.right, sum - root.val);
11     }
12 }
13 
14 /* 层次 */
15 public class JZ82_2
16 {
17     public static boolean hasPathSum(TreeNode root, int sum)
18     {
19         if (root == null) return false;
20         Queue<TreeNode> queue = new LinkedList<>();
21         queue.add(root);
22         while (!queue.isEmpty())
23         {
24             TreeNode pollNode = queue.poll();
25             if (pollNode.left != null)
26             {
27                 pollNode.left.val += pollNode.val;
28                 queue.add(pollNode.left);
29 
30             }
31             if (pollNode.right != null)
32             {
33                 pollNode.right.val += pollNode.val;
34                 queue.add(pollNode.right);
35             }
36             if (pollNode.val == sum && pollNode.left == null && pollNode.right == null)
37                 return true;
38         }
39         return false;
40     }
41 }

JZ34 二叉树中和为某一值的路径(二)

 1 /* DFS */
 2 public class JZ34_1
 3 {
 4     public static ArrayList<ArrayList<Integer>> res = new ArrayList<ArrayList<Integer>>();
 5 
 6     public static ArrayList<ArrayList<Integer>> FindPath(TreeNode root, int target)
 7     {
 8         if (root == null) return res;
 9         dfs(root, target, new ArrayList<Integer>());
10         return res;
11     }
12 
13     public static void dfs(TreeNode root, int target, ArrayList<Integer> path)
14     {
15         path.add(root.val);
16         target -= root.val;
17         if (root.left == null && root.right == null && target == 0)
18             res.add(new ArrayList<>(path));
19         if (root.left != null)
20             dfs(root.left, target, path);
21         if (root.right != null)
22             dfs(root.right, target, path);
23         path.remove(path.size() - 1);
24     }
25 }

标签:right,return,offer,int,null,root,public
From: https://www.cnblogs.com/VividBinGo/p/17721156.html

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