How to locate a specific difference between two strings in Python-CodePudding

I have a list of strings:

['oXoXXoo', 'oXXoooo', 'oooXooo']

These are moves of a puzzle where one peg jumps over an adjacent peg. The first item in the list is the starting state and the final item is the solved board.

I am trying to display the moves needed to solve the board in the format:

[ (4, L), (1, R) ]

where peg at index [4] jumps left to get to the second board state and peg at index [1] jumps right to solve the puzzle. Basically I need to find specific differences between each list item and return a tuple list based on them. My current pseudocode idea is:

find where oXX became Xoo
    path.add((index of the o 2, L))
find where XXo became ooX
    path.add((index of the X 2, R))

I have also considered turning the strings into a list and doing something with .difference but im not sure where to go from there. Any suggests into how I can compare strings or lists in python welcome!

CodePudding user response：

Something like this would probably work if I understood your problem correctly:

l = ['oXoXXoo', 'oXXoooo', 'oooXooo']
path = []
for i in range(len(l) - 1):
    before = l[i]
    after = l[i 1]
    assert len(before) == len(after)
    string_length = len(before)
    left = False
    right = False
    for j in range(string_length):
        if before[j] != after[j] and before[j] == "o":
            # It means that the peg went LEFT!
            left = True
            x = j
            break
        if before[j] != after[j] and before[j] == "X":
            # It means that the peg went RIGHT!
            right = True
            x = j
            break

    if right:
        path.append((x,"R"))
    if left:
        path.append((x 2,"L"))

for p in path:
    print(p)

Output:

(4,L)
(1,R)

It's sufficient to check the first elements that differ in two consecutive strings, then we can both infer if the peg went LEFT or RIGHT and the original peg position.

CodePudding user response：

IIUC, you want a function that takes two strings, s1 and s2, and describes the move used to get from s1 to s2 - or in other words

describe_move('XXoXXoo', 'oXXXXoo') should return (0, 'R')

You could write such a function by checking for the position of ('o', 'X') and identifying the move as coming from 2 places off on either side -

def describe_move(s1, s2):
    move = list(zip(s1, s2))
    peg_final_index = move.index(('o', 'X'))
    peg_initial_index = (peg_final_index   2) if move[peg_final_index   2] == ('X', 'o') else (peg_final_index - 2)
    direction = 'L' if peg_initial_index > peg_final_index else 'R'
    return peg_initial_index, direction

s1 = 'oXoXXoo'
s2 = 'oXXoooo'

describe_move(s1, s2)
# (4, 'L')

describe_move(s2, 'oooXooo')
# (1, 'R')

describe_move('XXoXXoo', 'oXXXXoo')
# (0, 'R')