LeetCode知识点总结 - 955

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最新推荐文章于 2024-02-14 19:09:20 发布

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给定一个字符串数组，题目要求通过删除某些列使数组在字典序下排列。解决方案是遍历数组，使用布尔数组记录每一列是否已排序，若发现不连续的有序子数组，则增加删除次数。返回最少删除次数。

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LeetCode 955. Delete Columns to Make Sorted II

考点	难度
Greedy	Easy

题目

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

We may choose any deletion indices, and we delete all the characters in those indices for each string.

For example, if we have strs = [“abcdef”,“uvwxyz”] and deletion indices {0, 2, 3}, then the final array after deletions is [“bef”, “vyz”].

Suppose we chose a set of deletion indices answer such that after deletions, the final array has its elements in lexicographic order (i.e., strs[0] <= strs[1] <= strs[2] <= … <= strs[n - 1]). Return the minimum possible value of answer.length.

思路

如果 A[i] < A[i + 1]，boolean array sorted[i] = true。对于每一列，如果有unsorted rows就删掉这一列。

答案

class Solution(object):
    def minDeletionSize(self, A):
        res, n, m = 0, len(A), len(A[0])
        is_sorted = [0] * (n - 1)
        for j in range(m):
            is_sorted2 = is_sorted[:]
            for i in range(n - 1):
                if A[i][j] > A[i + 1][j] and is_sorted[i] == 0:
                    res += 1
                    break
                is_sorted2[i] |= A[i][j] < A[i + 1][j]
            else:
                is_sorted = is_sorted2
        return res