The task of generating randomstrings until a given string is generated involves using random combinations of characters and progressively improving the string through mutations until the target string is matched.For example, given a target string like "geek," the goal is to keep generating random strings until one exactly matches "geek."
Using genetic algorithm
Genetic Algorithm is an evolutionary approach where we generate a random string and progressively improve it through mutation. Instead of completely regenerating a new string every time, we modify the existing one by changing one character at a time, ensuring each change brings us closer to the target.
Pythonimportstringimportrandom# Possible characterspossibleCharacters=string.ascii_lowercase+string.digits+ \string.ascii_uppercase+' ., !?;:'# Target stringt="geek"# Generate initial random stringdefgenerate_random_string(length):return''.join(random.choice(possibleCharacters)for_inrange(length))# Fitness function: count matching charactersdeffitness(current):returnsum(1fora,binzip(current,t)ifa==b)# Mutation function: change one random characterdefmutate(parent):index=random.randint(0,len(parent)-1)child=list(parent)child[index]=random.choice(possibleCharacters)return''.join(child)# Main evolution loopattempt=generate_random_string(len(t))iteration=0whileattempt!=t:print(attempt)new_attempt=mutate(attempt)# Keep the mutation only if it improves fitnessiffitness(new_attempt)>=fitness(attempt):attempt=new_attemptiteration+=1print(f"Target matched after{iteration} iterations")Output
FyFJ
.:YZ
aubo
.
.
.
g56G
gk6R
g7Se
gT o
gD d
gXek
g0ek
g ek
.
.
gUek
giek
geek
Target matched after 168 iterations
Explanation:
- Generates Random String creates an initial random string of the same length ast.
- Defines Fitness Function counts matching characters in the correct positions.
- Mutation Function changes one random character in the string
- Main Evolution Loopstarts with a random string, mutates it, compares fitness, accepts the mutation if fitness is maintained or improved, and repeats until the target is matched.
Using hill climbing approach
TheHill Climbing Algorithm takes a greedy approach by fixing correct characters and modifying only the incorrect ones. This ensures that once a character is correctly positioned, it remains unchanged.
Pythonimportstringimportrandom# Possible characterspossibleCharacters=string.ascii_lowercase+string.digits+ \string.ascii_uppercase+' ., !?;:'# Target stringt="geek"# Generate initial random stringdefgenerate_random_string(length):return''.join(random.choice(possibleCharacters)for_inrange(length))# Fitness functiondeffitness(current):returnsum(1fora,binzip(current,t)ifa==b)# Main hill-climbing loopattempt=generate_random_string(len(t))iteration=0whileattempt!=t:print(attempt)new_attempt=list(attempt)foriinrange(len(t)):ifnew_attempt[i]!=t[i]:new_attempt[i]=random.choice(possibleCharacters)iffitness(''.join(new_attempt))<fitness(attempt):new_attempt[i]=attempt[i]# Revert change if worseattempt=''.join(new_attempt)iteration+=1print(f"Target matched after{iteration} iterations")Output :
FyFJ
.:YZ
aubo
.
.
.
g56G
gk6R
g7Se
gT o
gD d
gXek
g0ek
g ek
.
.
gUek
giek
geek
Target matched after 168 iterations
Explanation:
- new_attempt list:This approach starts by converting the string to a list, allowing individual character manipulation.
- Hill Climbing iterates through each character in the current string, replacing non-matching characters with random ones, and reverts any changes that reduce fitness, ensuring that only improvements or unchanged states are kept.
Using iterative approach
This approach generates an initial random string and progressively replaces incorrect characters with random choices until the entire string matches the target.
Python# Importing string, random, and time modulesimportstringimportrandomimporttime# All possible characters including lowercase, uppercase, and special symbolspossibleCharacters=string.ascii_lowercase+string.digits+ \string.ascii_uppercase+' ., !?;:'# String to be generatedt="geek"# To take input from the user# t = input(str("Enter your target text: "))attemptThis=''.join(random.choice(possibleCharacters)foriinrange(len(t)))attemptNext=''completed=Falseiteration=0# Iterate while completed is falsewhilecompleted==False:print(attemptThis)attemptNext=''completed=True# Fix the index if matches with the string to be generatedforiinrange(len(t)):ifattemptThis[i]!=t[i]:completed=FalseattemptNext+=random.choice(possibleCharacters)else:attemptNext+=t[i]# Increment the iterationiteration+=1attemptThis=attemptNexttime.sleep(0.1)# Driver Codeprint("Target matched after "+str(iteration)+" iterations")Output :
FyFJ
.:YZ
aubo
.
.
.
g56G
gk6R
g7Se
gT o
gD d
gXek
g0ek
g ek
.
.
gUek
giek
geek
Target matched after 168 iterations
Explanation:
- attemptThisstarts with a random string.
- For each incorrect character in attemptThis, it is replaced with a random character.
- If the character is already correct, it is preserved.
- This process repeats until the entire string matches the target string.
- time.sleep(0.1) adds a slight delay to visualize the process.