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数据结构与算法之二叉树的先序遍历，中序遍历，后序遍历
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數(shù)據(jù)結(jié)構(gòu)與算法之二叉樹的先序遍歷，中序遍歷，后移遍歷
目錄
實(shí)現(xiàn)二叉樹的先序，中序，后序遍歷，包括遞歸方式和非遞歸方式在二叉樹中找到一個(gè)節(jié)點(diǎn)的后繼節(jié)點(diǎn)
1. 實(shí)現(xiàn)二叉樹的先序，中序，后序遍歷，包括遞歸方式和非遞歸方式
1. 先序遍歷，中序遍歷，后序遍歷遞歸版
public static void preOrderRecur(Node head
) {if (head
== null
) {return;}System
.out
.print(head
.value
+ " ");preOrderRecur(head
.left
);preOrderRecur(head
.right
);}public static void inOrderRecur(Node head
) {if (head
== null
) {return;}inOrderRecur(head
.left
);System
.out
.print(head
.value
+ " ");inOrderRecur(head
.right
);}public static void posOrderRecur(Node head
) {if (head
== null
) {return;}posOrderRecur(head
.left
);posOrderRecur(head
.right
);System
.out
.print(head
.value
+ " ");}
2. 先序遍歷，中序遍歷，后序遍歷非遞歸版
public static void preOrderUnRecur(Node head
) {System
.out
.print("pre-order: ");if (head
!= null
) {Stack
<Node> stack
= new Stack<Node>();stack
.add(head
);while (!stack
.isEmpty()) {head
= stack
.pop();System
.out
.print(head
.value
+ " ");if (head
.right
!= null
) {stack
.push(head
.right
);}if (head
.left
!= null
) {stack
.push(head
.left
);}}}System
.out
.println();}public static void inOrderUnRecur(Node head
) {System
.out
.print("in-order: ");if (head
!= null
) {Stack
<Node> stack
= new Stack<Node>();while (!stack
.isEmpty() || head
!= null
) {if (head
!= null
) {stack
.push(head
);head
= head
.left
;} else {head
= stack
.pop();System
.out
.print(head
.value
+ " ");head
= head
.right
;}}}System
.out
.println();}public static void posOrderUnRecur1(Node head
) {System
.out
.print("pos-order: ");if (head
!= null
) {Stack
<Node> s1
= new Stack<Node>();Stack
<Node> s2
= new Stack<Node>();s1
.push(head
);while (!s1
.isEmpty()) {head
= s1
.pop();s2
.push(head
);if (head
.left
!= null
) {s1
.push(head
.left
);}if (head
.right
!= null
) {s1
.push(head
.right
);}}while (!s2
.isEmpty()) {System
.out
.print(s2
.pop().value
+ " ");}}System
.out
.println();}public static void posOrderUnRecur2(Node h
) {System
.out
.print("pos-order: ");if (h
!= null
) {Stack
<Node> stack
= new Stack<Node>();stack
.push(h
);Node c
= null
;while (!stack
.isEmpty()) {c
= stack
.peek();if (c
.left
!= null
&& h
!= c
.left
&& h
!= c
.right
) {stack
.push(c
.left
);} else if (c
.right
!= null
&& h
!= c
.right
) {stack
.push(c
.right
);} else {System
.out
.print(stack
.pop().value
+ " ");h
= c
;}}}System
.out
.println();}
3. 先序，中序，后序遍歷非遞歸解析
先序遍歷
1. 如果節(jié)點(diǎn)不為null，則參加棧來存儲(chǔ)節(jié)點(diǎn)。
2. 先將頭節(jié)點(diǎn)添加到棧。
3. 當(dāng)棧不為null時(shí)，從棧中彈出一個(gè)頭節(jié)點(diǎn)
4. 由棧特性先進(jìn)后出和先序遍歷中左右知，先添加右節(jié)點(diǎn)，再添加左節(jié)點(diǎn)，這樣彈出的時(shí)候就是先左節(jié)點(diǎn)，然后右節(jié)點(diǎn)。
中序遍歷
如果head不為null，則創(chuàng)建棧結(jié)構(gòu)進(jìn)行存儲(chǔ)。當(dāng)棧或者h(yuǎn)ead不為null時(shí)，如果head不為null，則將它的左孩子全部壓入棧。當(dāng)head==null時(shí)，則彈出棧頂節(jié)點(diǎn)，將head指向它的右孩子。總結(jié)就是：當(dāng)前節(jié)點(diǎn)為null，從棧中拿一個(gè)節(jié)點(diǎn)，打印，當(dāng)前節(jié)點(diǎn)向右移。當(dāng)前節(jié)點(diǎn)不為null，將它壓入棧，當(dāng)前節(jié)點(diǎn)向左移； 后序遍歷
由先序遍歷為中左右，后序遍歷為左右中，我們可以通過兩個(gè)棧，使進(jìn)入棧1的順序?yàn)橹杏易?#xff0c;然后將棧1元素放入棧2，就實(shí)現(xiàn)了左右中的結(jié)構(gòu)。如果head不為null，創(chuàng)建兩個(gè)棧s1，s2,。將head先壓入s1。當(dāng)棧s1不為null時(shí)，棧s1彈出一個(gè)元素，將彈出的元素加入棧s2（即先序遍歷打印的位置）判斷head左節(jié)點(diǎn)是否為null，不為null就加入s1，判斷head右節(jié)點(diǎn)是否為null，不為null就加入s1.（先加左，后加右，出來就是先右，后左）打印出s2中的元素即可。
2. 在二叉樹中找到一個(gè)節(jié)點(diǎn)的后繼節(jié)點(diǎn)
題目描述
思路：
node節(jié)點(diǎn)如果有右孩子，則右孩子的最左節(jié)點(diǎn)就是后繼節(jié)點(diǎn)。如1的后繼節(jié)點(diǎn)是右孩子3的最左節(jié)點(diǎn)6node節(jié)點(diǎn)如果沒有右孩子，則往上找，找到當(dāng)前節(jié)點(diǎn)是父節(jié)點(diǎn)的左孩子就停，那個(gè)父節(jié)點(diǎn)就是后繼節(jié)點(diǎn)。如5的后繼節(jié)點(diǎn)是1的左孩子是2，所以5的后繼節(jié)點(diǎn)是1 備注：前驅(qū)的找法：
node節(jié)點(diǎn)如果有左孩子，那么左孩子最右節(jié)點(diǎn)就是前驅(qū)節(jié)點(diǎn)，如1的前驅(qū)節(jié)點(diǎn)是左孩子2的最右節(jié)點(diǎn)5如果node節(jié)點(diǎn)沒有左孩子，則往上找，找到當(dāng)前節(jié)點(diǎn)是父節(jié)點(diǎn)的右孩子就停，那個(gè)父節(jié)點(diǎn)就是前驅(qū)節(jié)點(diǎn)，如6的前驅(qū)節(jié)點(diǎn)是1的右孩子3，所以6的前驅(qū)節(jié)點(diǎn)是1
代碼實(shí)現(xiàn)
public class Code_SuccessorNode {public static class Node {public int value
;public Node left
;public Node right
;public Node parent
;public Node(int data
) {this.value
= data
;}}public static Node
getSuccessorNode(Node node
) {if (node
== null
) {return node
;}if (node
.right
!= null
) {return getLeftMost(node
.right
);} else {Node parent
= node
.parent
;while (parent
!= null
&& parent
.left
!= node
) {node
= parent
;parent
= node
.parent
;}return parent
;}}public static Node
getLeftMost(Node node
) {if (node
== null
) {return node
;}while (node
.left
!= null
) {node
= node
.left
;}return node
;}public static void main(String
[] args
) {Node head
= new Node(6);head
.parent
= null
;head
.left
= new Node(3);head
.left
.parent
= head
;head
.left
.left
= new Node(1);head
.left
.left
.parent
= head
.left
;head
.left
.left
.right
= new Node(2);head
.left
.left
.right
.parent
= head
.left
.left
;head
.left
.right
= new Node(4);head
.left
.right
.parent
= head
.left
;head
.left
.right
.right
= new Node(5);head
.left
.right
.right
.parent
= head
.left
.right
;head
.right
= new Node(9);head
.right
.parent
= head
;head
.right
.left
= new Node(8);head
.right
.left
.parent
= head
.right
;head
.right
.left
.left
= new Node(7);head
.right
.left
.left
.parent
= head
.right
.left
;head
.right
.right
= new Node(10);head
.right
.right
.parent
= head
.right
;Node test
= head
.left
.left
;System
.out
.println(test
.value
+ " next: " + getSuccessorNode(test
).value
);test
= head
.left
.left
.right
;System
.out
.println(test
.value
+ " next: " + getSuccessorNode(test
).value
);test
= head
.left
;System
.out
.println(test
.value
+ " next: " + getSuccessorNode(test
).value
);test
= head
.left
.right
;System
.out
.println(test
.value
+ " next: " + getSuccessorNode(test
).value
);test
= head
.left
.right
.right
;System
.out
.println(test
.value
+ " next: " + getSuccessorNode(test
).value
);test
= head
;System
.out
.println(test
.value
+ " next: " + getSuccessorNode(test
).value
);test
= head
.right
.left
.left
;System
.out
.println(test
.value
+ " next: " + getSuccessorNode(test
).value
);test
= head
.right
.left
;System
.out
.println(test
.value
+ " next: " + getSuccessorNode(test
).value
);test
= head
.right
;System
.out
.println(test
.value
+ " next: " + getSuccessorNode(test
).value
);test
= head
.right
.right
; System
.out
.println(test
.value
+ " next: " + getSuccessorNode(test
));}}
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