Generating random strings until a given string is generated (original) (raw)

Last Updated : 2 Feb, 2026

Given a target string 'S', the task is to generate random strings of the same length as 'S' until the generated string exactly matches the target. **For Example:

**Input: hello

**Output:
jfus
flsf
sowe
hello
Target matched after 3 iterations

Let's look at the different methods below:

Genetic Algorithm

This approach starts with a random string and slowly evolves it toward the target string. It changes one character at a time and only keeps changes that make the string closer to the target.

Python `

import string import random

chars = string.ascii_letters + string.digits + ' .,!?;:' target = "geeks"

s = ''.join(random.choice(chars) for _ in range(len(target))) iterations = 0

while s != target: print(s) 

i = random.randint(0, len(s)-1)
l = list(s)
l[i] = random.choice(chars)
s1 = ''.join(l)

if sum(a == b for a, b in zip(s1, target)) >= sum(a == b for a, b in zip(s, target)):
    s = s1

iterations += 1

print(s)
print(f"Target matched after {iterations} iterations")

`

**Output

geDjs
geDjs
geDjs
geD2s
geD2s
geD2s
......
geek
Target matched after 1307 iterations

**Explanation:

Hill Climbing Approach

This approach starts with a random string and gradually improves it by fixing the correct characters and only changing the incorrect ones. Any change that reduces correctness is discarded, so the string slowly climbs toward the target.

Python `

import string import random

chars = string.ascii_letters + string.digits + ' .,!?;:' target = "geek"

a = ''.join(random.choice(chars) for _ in range(len(target))) iterations = 0

while a != target: print(a) b = list(a)

for i in range(len(target)):
    if b[i] != target[i]:
        b[i] = random.choice(chars)
        if sum(x == y for x, y in zip(''.join(b), target)) < sum(x == y for x, y in zip(a, target)):
            b[i] = a[i]

a = ''.join(b)
iterations += 1

print(a)
print(f"Target matched after {iterations} iterations")

`

**Output

sx18
1EEp
mzhm
8JQN
SeLb
......
geek
Target matched after 113 iterations

**Explanation:

Iterative Character Replacement

In this approach, we start with a random string and repeatedly replace only the incorrect characters with random choices, keeping correct characters unchanged, until the string matches the target.

Python `

import string import random import time

chars = string.ascii_letters + string.digits + ' .,!?;:' t = "geek"

s = ''.join(random.choice(chars) for _ in range(len(t))) done = False it = 0

while not done: print(s) s1 = '' done = True

for i in range(len(t)):
    if s[i] != t[i]:
        done = False
        s1 += random.choice(chars)
    else:
        s1 += t[i]

s = s1
it += 1

print(f"Target matched after {it} iterations")

`

**Output

vkZ2
tac4
I56g
zqPR
9XuS
.....
geek
Target matched after 114 iterations

**Explanation:

Pure Random

In this approach, a completely random string is generated in each iteration until it exactly matches the target string.

Python `

import random, string

target = "geek" chars = string.ascii_letters + string.digits + ' .,!?;:'

s = ''.join(random.choice(chars) for _ in range(len(target))) iterations = 0

while s != target: print(s)
s = ''.join(random.choice(chars) for _ in range(len(target)))
iterations += 1

print(s)
print(f"Target matched after {iterations} iterations")

`

**Output

g5ek
gUek
gWek
gXek
gOek
gWek
......
geek
Target matched after 1104 iterations

**Explanation: