[leetcode] 859. Buddy Strings @ python

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原题

Given two strings A and B of lowercase letters, return true if and only if we can swap two letters in A so that the result equals B.

Example 1:

Input: A = “ab”, B = “ba”
Output: true
Example 2:

Input: A = “ab”, B = “ab”
Output: false
Example 3:

Input: A = “aa”, B = “aa”
Output: true
Example 4:

Input: A = “aaaaaaabc”, B = “aaaaaaacb”
Output: true
Example 5:

Input: A = “”, B = “aa”
Output: false

Note:

0 <= A.length <= 20000
0 <= B.length <= 20000
A and B consist only of lowercase letters.

解法

排除法. 当A, B长度不相等时, 返回False. 然后遍历A, 将A与B字符不同的index放入diff. 符合题意的条件是diff的长度为0或者2. 当diff的长度为0时, 说明A与B相同, 那么A必须有重复字符才能交换字符得出B. 当diff的长度为2时, 尝试交换字符看能否得到B.

代码

class Solution(object):
    def buddyStrings(self, A, B):
        """
        :type A: str
        :type B: str
        :rtype: bool
        """
        if len(A) != len(B):
            return False        
        
        diff = []
        for i, ch in enumerate(A):
            if B[i] != ch:
                diff.append(i)
        if len(diff) not in [0,2]:
            return False
        if len(diff) == 0 and len(set(A)) < len(A):
            return True
        if len(diff) == 2:
            A_list = list(A)
            A_list[diff[0]], A_list[diff[1]] = A_list[diff[1]], A_list[diff[0]]
            if A_list == list(B):
                return True
        return False