Data structure (3) acwing

1. Hash table

Hash function concept:

(1) X mod 10 ^ 5, that is, the value range {modulus is reduced. It is best to takePrime numberThe probability of collision is minimal}

(2) Conflict resolution

• Find the first greater than IQualitative factor

1. storage structure

   • open addressing

     (the array length is 2 ~ 3 times) {operations involved: add, query and delete (just make a mark, not really delete)}

     • 

       

       0x3f3f3f3f3f is a number greater than 10 ^ 9. In the memset() function, it is stored by bytes. Because h is an int array and occupies 4 bytes, it is enough to write a 0x3f (one byte is 0x3f)

   • Zipper method

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2. String hash

• All string matching problems do not necessarily use KMP, but can also be usedString hashmode
• Usage scenario: compare whether two strings are equal
• KMP algorithm and string hash comparison: KMP is characterized by handling “circular knot”

The core is: take a string in k-ary form as a number

3.STL

1.vector

• Size(), number of elements

• Empty() returns whether it is empty

• Clear

• Front() / back() first / last element

• push_ back() / pop_ Back() insert a number to the back / delete the last number of the array

• Begin() / end() number 0 / number of the last numberLast number

  

  

Multiplication: when the system allocates space for a program, the time required is independent of the size of the space,Only related to the number of requests

2.string

• Size(), number of elements
• Empty() returns whether it is empty
• Clear
• Substr(): intercept string
• c_ Str(): the first subscript of the string

Initial subscript is 0

3.queue

• empty()

• size()

• Push (): inserts an element at the end of the queue

• Front(): returns the queue header element

• Back(): returns the end of queue element

• Pop (): pop up the queue header element

4.priority_ Queue (heap)

The default is large root heap, which is converted toSmall root pileThe way

• Push (): insert an element
• Top (): returns the heap top element
• Pop(): pop the top of heap element

5.stack

• empty()

• size()

• push()

• top()

• pop()

6. Deque (double ended queue) — basically not use

Equivalent to enhanced vector

7.set、multiset、map、multimap

Size (), empty (), clear (), begin () / end () + +, – return the predecessor and successor, time complexity O (logn)

• set/multiset

• map/multimap

• unordered_set,unordered_map,unordered_multiset,unordered_multimap

  ​ It is similar to the above, but the time complexity of adding, deleting, modifying and querying is O (1)

  ​ Lower is not supported_ bound() / upper_ Bound (), iterator + +–

• BitSet pressure