Program to shuffle string with given indices in Python

Suppose we have a string s and a list of indices ind, they are of same length. The string s will be shuffled such that the character at position i moves to indices[i] in the final string. We have to find the final string.

So, if the input is like s = "ktoalak" and ind = [0,5,1,6,2,4,3], then the output will be "kolkata".

To solve this, we will follow these steps ?

• fin_str := a list whose size is same as s and fill with empty strings

• for each index i and character v in s, do

  • fin_str[ind[i]] := v

• join each character present in fin_str and return

Example

Let us see the following implementation to get better understanding ?

def solve(s, ind):
    fin_str = [''] * len(s)
    for i, v in enumerate(s):
        fin_str[ind[i]] = v
    
    return "".join(fin_str)

s = "ktoalak"
ind = [0,5,1,6,2,4,3]
print(solve(s, ind))

kolkata

Step-by-Step Breakdown

Let's trace through the algorithm with our example ?

def solve_with_steps(s, ind):
    print(f"Original string: {s}")
    print(f"Indices mapping: {ind}")
    
    fin_str = [''] * len(s)
    print(f"Initial result array: {fin_str}")
    
    for i, v in enumerate(s):
        fin_str[ind[i]] = v
        print(f"Step {i+1}: Place '{v}' at position {ind[i]} ? {fin_str}")
    
    result = "".join(fin_str)
    print(f"Final result: {result}")
    return result

s = "ktoalak"
ind = [0,5,1,6,2,4,3]
solve_with_steps(s, ind)

Original string: ktoalak
Indices mapping: [0, 5, 1, 6, 2, 4, 3]
Initial result array: ['', '', '', '', '', '', '']
Step 1: Place 'k' at position 0 ? ['k', '', '', '', '', '', '']
Step 2: Place 't' at position 5 ? ['k', '', '', '', '', 't', '']
Step 3: Place 'o' at position 1 ? ['k', 'o', '', '', '', 't', '']
Step 4: Place 'a' at position 6 ? ['k', 'o', '', '', '', 't', 'a']
Step 5: Place 'l' at position 2 ? ['k', 'o', 'l', '', '', 't', 'a']
Step 6: Place 'a' at position 4 ? ['k', 'o', 'l', '', 'a', 't', 'a']
Step 7: Place 'k' at position 3 ? ['k', 'o', 'l', 'k', 'a', 't', 'a']
Final result: kolkata

Alternative Approach Using Dictionary

We can also solve this using a dictionary for cleaner code ?

def solve_dict(s, ind):
    char_map = {ind[i]: char for i, char in enumerate(s)}
    return "".join(char_map[i] for i in range(len(s)))

s = "ktoalak"
ind = [0,5,1,6,2,4,3]
print(solve_dict(s, ind))

kolkata

Conclusion

String shuffling with indices involves creating a new array and placing each character at its designated position. Both the list-based and dictionary approaches provide efficient solutions with O(n) time complexity.