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S3Q2 · String Rearrangement

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Type: File-in, stdout-out

Core idea: split each line on ",", first part is the string, remaining parts are 1-based indices specifying the new character order.

import tempfile, sys

_, filename = tempfile.mkstemp(prefix="case")
with open(filename, 'w') as f:
    f.write(sys.stdin.read())

with open(filename) as f:
    for line in f:
        line = line.strip()
        if not line:
            continue
        parts   = line.split(",")
        s       = parts[0]
        indices = [int(i) - 1 for i in parts[1:]]   # convert to 0-based
        print("".join(s[i] for i in indices))

Key rules: - Line format: string,i1,i2,i3,... - Indices are 1-based → subtract 1 for 0-based access - Characters are rearranged in the order given by the indices - Skip blank lines

Problem Statement

Problem (File I/O → stdout)

Read a file where each line contains a string followed by comma-separated 1-based indices. Print each string rearranged according to the given index order.

Example:

Input file 
hello,2,1,3,5,4
abcdef,3,2,1,6,5,4
xyz,3,1,2
Output 
ehlol
cbafed
zxy

Tracing all examples

Line 1: hello,2,1,3,5,4 

s = "hello"    (h=0, e=1, l=2, l=3, o=4)
indices = [2,1,3,5,4] → 0-based: [1,0,2,4,3]

s[1]=e, s[0]=h, s[2]=l, s[4]=o, s[3]=l
→ "ehlol" ✓

Line 2: abcdef,3,2,1,6,5,4 

s = "abcdef"   (a=0, b=1, c=2, d=3, e=4, f=5)
indices → 0-based: [2,1,0,5,4,3]

s[2]=c, s[1]=b, s[0]=a, s[5]=f, s[4]=e, s[3]=d
→ "cbafed" ✓

Line 3: xyz,3,1,2 

s = "xyz"    (x=0, y=1, z=2)
indices → 0-based: [2,0,1]

s[2]=z, s[0]=x, s[1]=y
→ "zxy" ✓

Solution approaches

import tempfile, sys

_, filename = tempfile.mkstemp(prefix="case")
with open(filename, 'w') as f:
    f.write(sys.stdin.read())

with open(filename) as f:
    for line in f:
        line = line.strip()
        if not line:
            continue
        parts   = line.split(",")
        s       = parts[0]
        indices = [int(i) - 1 for i in parts[1:]]
        print("".join(s[i] for i in indices))

import tempfile, sys

_, filename = tempfile.mkstemp(prefix="case")
with open(filename, 'w') as f:
    f.write(sys.stdin.read())

with open(filename) as f:
    for line in f:
        line = line.strip()
        if not line:
            continue

        parts  = line.split(",")
        s      = parts[0]           # the string to rearrange
        result = []

        for idx_str in parts[1:]:
            idx = int(idx_str) - 1  # convert 1-based to 0-based
            result.append(s[idx])

        print("".join(result))

import tempfile, sys

_, filename = tempfile.mkstemp(prefix="case")
with open(filename, 'w') as f:
    f.write(sys.stdin.read())

with open(filename) as f:
    for line in f:
        line = line.strip()
        if not line:
            continue
        parts   = line.split(",")
        s       = parts[0]
        indices = list(map(lambda x: int(x) - 1, parts[1:]))
        print("".join(map(lambda i: s[i], indices)))

Key takeaways

01

1-based to 0-based: subtract 1

The indices in the file are 1-based (position 1 = first character). Python strings are 0-based. Always subtract 1 before using the index: int(i) - 1.

02

parts[0] is the string, parts[1:] are the indices

Splitting on "," gives the string as the first element and index strings as the rest. parts[1:] slices off everything after the string cleanly.

03

Skip blank lines

Files often end with a trailing newline, creating an empty line. Checking if not line: continue after stripping prevents an error when trying to split an empty string.