【leetcode】1540. Can Convert String in K Moves

题目如下：

Given two strings s and t, your goal is to convert s into t in k moves or less.

During the ith (1 <= i <= k) move you can:

• Choose any index j (1-indexed) from s, such that 1 <= j <= s.length and j has not been chosen in any previous move, and shift the character at that index i times.
• Do nothing.

Shifting a character means replacing it by the next letter in the alphabet (wrapping around so that 'z' becomes 'a'). Shifting a character by i means applying the shift operations i times.

Remember that any index j can be picked at most once.

Return true if it's possible to convert s into t in no more than k moves, otherwise return false.

Example 1:

Input: s = "input", t = "ouput", k = 9
Output: true
Explanation: In the 6th move, we shift 'i' 6 times to get 'o'. And in the 7th move we shift 'n' to get 'u'.

Example 2:

Input: s = "abc", t = "bcd", k = 10
Output: false
Explanation: We need to shift each character in s one time to convert it into t. We can shift 'a' to 'b' during the 1st move. 
However, there is no way to shift the other characters in the remaining moves to obtain t from s.

Example 3:

Input: s = "aab", t = "bbb", k = 27
Output: true
Explanation: In the 1st move, we shift the first 'a' 1 time to get 'b'. In the 27th move, we shift the second 'a' 27 times 
to get 'b'. 

Constraints:

• 1 <= s.length, t.length <= 10^5
• 0 <= k <= 10^9
• s, t contain only lowercase English letters.

解题思路：统计出s中每个字符转成成t中对应的字符所需要的转换次数，如果需要转换i次的字符的数量一个有v个，那么需要满足 i + (v-1)*26 > k 。

代码如下：

class Solution(object):
    def canConvertString(self, s, t, k):
        """
        :type s: str
        :type t: str
        :type k: int
        :rtype: bool
        """
        if len(s) != len(t):return False
        count = [0] * 27
        for (c1,c2) in zip(s,t):
            if c1 <= c2:
                count[ord(c2) - ord(c1)] += 1
            else:
                count[26 - (ord(c1) - ord(c2))] += 1
        for i,v in enumerate(count):
            if i > 0 and i + (v-1)*26 > k:
                return False

        return True