ADVANCED DATA STRUCTURES PROGRAM • LEVEL 18 — ADVANCED HASHING

Build an LRU Cache with Hashing and a List

Learn how to build an lru cache with hashing and a list using a clear C program.

AdvancedCollision resolutionHash-table design

PROBLEM UNDERSTANDING

Input and expected output

Sample input
No input required
Sample output
Get1=10 Get2=-1 Get3=30

COMPLETE C PROGRAM

Complete C implementation

ads-lru-cache-hash-list.c
Open in compiler
#include <stdio.h>

struct Cache{int keys[2],values[2],count;};int find(struct Cache*c,int key){for(int i=0;i<c->count;i++)if(c->keys[i]==key)return i;return -1;}void touch(struct Cache*c,int index){int k=c->keys[index],v=c->values[index];for(int i=index;i>0;i--){c->keys[i]=c->keys[i-1];c->values[i]=c->values[i-1];}c->keys[0]=k;c->values[0]=v;}int get(struct Cache*c,int key){int i=find(c,key);if(i<0)return -1;int value=c->values[i];touch(c,i);return value;}void put(struct Cache*c,int key,int value){int i=find(c,key);if(i>=0){c->values[i]=value;touch(c,i);return;}if(c->count<2)c->count++;for(i=c->count-1;i>0;i--){c->keys[i]=c->keys[i-1];c->values[i]=c->values[i-1];}c->keys[0]=key;c->values[0]=value;}

int main(void)
{
    struct Cache cache={{0},{0},0};put(&cache,1,10);put(&cache,2,20);printf("Get1=%d ",get(&cache,1));put(&cache,3,30);printf("Get2=%d Get3=%d\n",get(&cache,2),get(&cache,3));return 0;
}

GUIDED CODE TOUR • NOT LIVE EXECUTION

Study the program line by line

Use the real compiler button above to run and debug with different inputs.

CURRENT STEP

Select Start to walk through the important lines.

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EXPECTED OUTPUT FOR THE SAMPLE

Get1=10 Get2=-1 Get3=30
0%Step 0 of 0

PROGRAM EXPLANATION

Algorithm and explanation

  1. Read the required input values.
  2. Move every accessed key to the front and evict the least-recent key from the back.
  3. Display the computed result.

Move every accessed key to the front and evict the least-recent key from the back.

EFFICIENCY

Time and space complexity

Time complexity

O(1) with a real hash map and doubly linked list

Auxiliary space

O(capacity)

DEBUGGING CHECKLIST

Common mistakes

Check this

Use the correct format specifier for every variable.

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Initialize variables before using their values.

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Check braces, semicolons and input order carefully.

Try it yourself

Practice: Run the program with the sample input, predict its output, and then test one boundary case of your own.