php 二叉树

https://blog.youkuaiyun.com/nuli888/article/details/52181785

php实现先序、中序、后序遍历二叉树

2016年08月11日 13:30:42 爱代码也爱生活 阅读数：8270更多

个人分类： php算法

版权声明：本文为博主原创文章，未经博主允许不得转载。 https://blog.youkuaiyun.com/nuli888/article/details/52181785

二叉树是每个节点最多有两个子树的树结构。通常子树被称作“左子树”（left subtree）和“右子树”（right subtree）。二叉树常被用于实现二叉查找树和二叉堆

 

1. <?php

2. class Node{

3. public $value;

4. public $left;

5. public $right;

6. }

7. //先序遍历 根节点 ---> 左子树 ---> 右子树

8. function preorder($root){

9. $stack=array();

10. array_push($stack,$root);

11. while(!empty($stack)){

12. $center_node=array_pop($stack);

13. echo $center_node->value.' ';//先输出根节点

14. if($center_node->right!=null){

15. array_push($stack,$center_node->right);//压入左子树

16. }

17. if($center_node->left!=null){

18. array_push($stack,$center_node->left);

19. }

20. }

21. }

22. //中序遍历，左子树---> 根节点 ---> 右子树

23. function inorder($root){

24. $stack = array();

25. $center_node = $root;

26. while (!empty($stack) || $center_node != null) {

27. while ($center_node != null) {

28. array_push($stack, $center_node);

29. $center_node = $center_node->left;

30. }

31.  

32. $center_node = array_pop($stack);

33. echo $center_node->value . " ";

34.  

35. $center_node = $center_node->right;

36. }

37. }

38. //后序遍历，左子树 ---> 右子树 ---> 根节点

39. function tailorder($root){

40. $stack=array();

41. $outstack=array();

42. array_push($stack,$root);

43. while(!empty($stack)){

44. $center_node=array_pop($stack);

45. array_push($outstack,$center_node);//最先压入根节点，最后输出

46. if($center_node->left!=null){

47. array_push($stack,$center_node->left);

48. }

49. if($center_node->right!=null){

50. array_push($stack,$center_node->right);

51. }

52. }

53.  

54. while(!empty($outstack)){

55. $center_node=array_pop($outstack);

56. echo $center_node->value.' ';

57. }

58.  

59. }

60. $a=new Node();

61. $b=new Node();

62. $c=new Node();

63. $d=new Node();

64. $e=new Node();

65. $f=new Node();

66. $a->value='A';

67. $b->value='B';

68. $c->value='C';

69. $d->value='D';

70. $e->value='E';

71. $f->value='F';

72. $a->left=$b;

73. $a->right=$c;

74. $b->left=$d;

75. $c->left=$e;

76. $c->right=$f;

77. preorder($a);//A B D C E F

78. echo '<hr/>';

79. inorder($a);//D B A E C F

80. echo '<hr/>';

81. tailorder($a);//D B E F C A

结果：

 

A B D C E F

---

D B A E C F

---

D B E F C A