Trie是一种有效的信息检索数据结构。使用Trie，可以使搜索复杂度达到最佳极限(密钥长度)。
试了一下。任务是以自下而上的方式打印字符
向上遍历：
First print string of left most subtree(from bottom to top) then print string of second left subtree(from bottom to top) then print for third left subtree and so on.
它类似于树的后遍历
例子：
Input :
root
/ \
a t
| |
n h
| \ |
s y e
| | \
w i r
| | |
e r e
|
r
Output : r, e, w, s, y, n, a, r, i, e, r, e, h, t
Input :
root
/ \
c t
| |
a h
| \ |
l t e
| | \
l i r
| \ | |
e i r e
| |
r n
|
g
Output : r, e, g, n, i, l, l, t, a, c, r, i, e, r, e, h, t解释 ：
在第一个示例中，根有两个部分。第一部分包含字符串：“答案”和“任何”。
第二部分使用字符串“ their”和“ there”。
- 现在，我们首先离开子树，其中包含用字符“ n”分隔的字符串“ answer”和“ any”。现在，“ n”将字符“ s”，“ w”，“ e”，“ r”和“ y”的两部分分开。因此，以相反的顺序打印“ s”，“ w”，“ e”，“ r”，然后打印“ y”并向上打印“ n”(分隔字符串)，然后向上打印“ a”。现在，左下子树以自下而上的方式打印“ r”，“ e”，“ w”，“ s”，“ y”，“ n”，“ a”。
- 对根的另一个子树执行相同的操作，该子树包含用字符“ e”分隔的字符串“ their”和“ there”。
方法 ：
这样做的想法是从trie的根节点开始遍历，每当我们找到NON-NULL子节点时，当我们得到“ NULL”时我们便递归地前进，我们简单地返回并打印当前节点的值，并且相同直到找到一个叶子节点(实际上是标记字符串的结尾)的节点。
下面是上述方法的实现：
CPP
// CPP program to traverse in bottom up manner
#include
using namespace std;
#define CHILDREN 26
#define MAX 100
// Trie node
struct trie {
trie* child[CHILDREN];
// endOfWord is true if the node represents
// end of a word
bool endOfWord;
};
// Function will return the new node(initialized to NULLs)
trie* createNode()
{
trie* temp = new trie();
temp->endOfWord = false;
for (int i = 0; i < CHILDREN; i++) {
// Initialise all child to the null, initially
temp->child[i] = NULL;
}
// Return newly created node
return temp;
}
// Function will insert the string in a trie recursively
void insertRecursively(trie* itr, string str, int i)
{
if (i < str.length()) {
int index = str[i] - 'a';
if (itr->child[index] == NULL) {
// Assining a newly created node
itr->child[index] = createNode();
}
// Recursive call for insertion
// of a string in a trie
insertRecursively(itr->child[index], str, i + 1);
}
else {
// Make the endOfWord true which represents
// the end of string
itr->endOfWord = true;
}
}
// Function call to insert a string
void insert(trie* itr, string str)
{
// Function call with necessary arguments
insertRecursively(itr, str, 0);
}
// Function to print traverse
// the tree in bottum to top manner
void printPattern(trie* itr)
{
// Base condition
if (itr == NULL)
return;
// Loop for printing t a value of character
for (int i = 0; i < CHILDREN; i++) {
// Recursive call for print pattern
printPattern(itr->child[i]);
if (itr->child[i] != NULL) {
char ch = (i + 97);
cout << ch << ", "; // Print character
}
}
}
// Driver code
int main()
{
trie* root = createNode();
// Function to insert a string
insert(root, "thier");
insert(root, "there");
insert(root, "answer");
insert(root, "any");
// Function call for printing a pattern
printPattern(root);
return 0;
} Python3
# Python3 program to traverse in bottom up manner
CHILDREN = 26
MAX = 100
# Trie node
class trie:
def __init__(self):
self.child = [None for i in range(CHILDREN)]
# endOfWord is true if the node represents
# end of a word
self.endOfWord = False
# Function will return the new node(initialized to NULLs)
def createNode():
temp = trie()
return temp
# Function will insert the string in a trie recursively
def insertRecursively(itr, str, i):
if (i < len(str)):
index = ord(str[i]) - ord('a')
if (itr.child[index] == None):
# Assining a newly created node
itr.child[index] = createNode()
# Recursive call for insertion
# of a string in a trie
insertRecursively(itr.child[index], str, i + 1)
else:
# Make the endOfWord true which represents
# the end of string
itr.endOfWord = True
# Function call to insert a string
def insert(itr, str):
# Function call with necessary arguments
insertRecursively(itr, str, 0)
# Function to print traverse
# the tree in bottum to top manner
def printPattern(itr):
# Base condition
if(itr == None):
return
# Loop for printing t a value of character
for i in range(CHILDREN):
# Recursive call for print pattern
printPattern(itr.child[i])
if (itr.child[i] != None):
ch = chr(i + 97)
# Print character
print(ch,end=', ')
# Driver code
if __name__=='__main__':
root = createNode()
# Function to insert a string
insert(root, "thier")
insert(root, "there")
insert(root, "answer")
insert(root, "any")
# Function call for printing a pattern
printPattern(root)
# This code is countributed by rutvik_56输出：
r, e, w, s, y, n, a, e, r, e, r, e, i, h, t,