[Leetcode] 194. Transpose File

最新推荐文章于 2019-04-19 15:28:29 发布

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本文介绍了一种处理文本文件的方法，即将文件的内容进行转置。针对每一行拥有相同数量的列的情况，提供了两种解决方案：一种是超出内存限制的简单实现；另一种是逐行读取和处理的高效方法。

Problem
Given a text file file.txt, transpose its content.

You may assume that each row has the same number of columns and each field is separated by the ’ ’ character.

For example, if file.txt has the following content:

name age
alice 21
ryan 30

Output the following:

name alice ryan
age 21 30

NOT Solution (exceeding memory limitation)

# Read from the file file.txt and print its transposed content to stdout.

cnt=$(sed '1q' file.txt | awk '{print NF}')
#or use `cnt=$(head -n1 file.txt | ...)` here.
for ((i=1;i<=$cnt;i=i+1))
do
echo $(cut -d ' ' -f $i file.txt)
done

According to above solution(exceeding memory limitation), we know that we cannot read the whole file in a time, we should read it and process it word by word, line by line.

solution(just like C)

awk '
{
    for (i = 1; i <= NF; i++) {
        if(NR == 1) {
            s[i] = $i;
        } else {
            s[i] = s[i] " " $i;
        }
    }
}
END {
    for (i = 1; s[i] != ""; i++) {
        print s[i];
    }
}' file.txt