[leetcode] 944. Delete Columns to Make Sorted

[leetcode] 944. Delete Columns to Make Sorted

Description

You are given an array of n strings strs, all of the same length.

The strings can be arranged such that there is one on each line, making a grid. For example, strs = [“abc”, “bce”, “cae”] can be arranged as:

abcbcecae

You want to delete the columns that are not sorted lexicographically. In the above example (0-indexed), columns 0 (‘a’, ‘b’, ‘c’) and 2 (‘c’, ‘e’, ‘e’) are sorted while column 1 (‘b’, ‘c’, ‘a’) is not, so you would delete column 1.

Return the number of columns that you will delete.

Example 1:

Input: strs = ["cba","daf","ghi"]Output: 1Explanation: The grid looks as follows: cba daf ghiColumns 0 and 2 are sorted, but column 1 is not, so you only need to delete 1 column.

Example 2:

Input: strs = ["a","b"]Output: 0Explanation: The grid looks as follows: a bColumn 0 is the only column and is sorted, so you will not delete any columns.

Example 3:

Input: strs = ["zyx","wvu","tsr"]Output: 3Explanation: The grid looks as follows: zyx wvu tsrAll 3 columns are not sorted, so you will delete all 3.

Constraints:

n == strs.length1 <= n <= 1001 <= strs[i].length <= 1000strs[i] consists of lowercase English letters.

分析

题目的意思是：给定一个字符串数组，把这些字符串排列成矩阵，删除那些没有按照字母顺序排序的列。

思路也很直接，直接把每一列取出来，然后排序后看是否和原来的字符串相等就可以判断了，然后统计一下不等的数量，维护更新res。

代码

class Solution: def minDeletionSize(self, strs: List[str]) -> int: res=0 for i in range(len(strs[0])): s=''.join(item[i] for item in strs) s1=''.join(sorted(s)) if(s!=s1): res+=1 return res

参考文献

​​Python Solution​​

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