Last Modified: 2017-08-25 10:53:10

• 193. Valid Phone Numbers
• 195. Tenth Line
• 192. Word Frequency
• 194. Tranpose File

193. Valid Phone Numbers

You may assume that a valid phone number must appear in one of the following two formats: (xxx) xxx-xxxx or xxx-xxx-xxxx. (x means a digit)

# Read from the file file.txt and output all valid phone numbers to stdout.
grep -E '^(([0-9]{3}-[0-9]{3}-[0-9]{4})|(\([0-9]{3}\) [0-9]{3}-[0-9]{4}))$' file.txt

195. Tenth Line

How would you print just the 10th line of a file?

# Read from the file file.txt and output the tenth line to stdout.
line_num=0
while read line && ((line_num < 10)); do
    line_num=$line_num+1
    if ((line_num == 10)); then
        echo $line
        break
    fi
done < file.txt

192. Word Frequency

# Read from the file words.txt and output the word frequency list to stdout.
declare -A freq
while read word; do
    ((++freq[$word]))
done < <(tr -s " " "\n" < words.txt)
# echo ${words[*]}
for word in ${!freq[*]}; do
    echo $word ${freq[$word]}
done | sort -k 2nbr

it seems that there some problems with shell array…

➜  ~ a+=1
➜  ~ a+=1
➜  ~ echo ${a[*]}
11
➜  ~ for i in ${a[*]}; do
for> echo $i
for> done
11
➜  ~ for i in ${a[@]}; do
for> echo $i
for> done
11
➜  ~ for i in "${a[@]}"; do
for> echo $i
for> done
11
➜  ~ for i in "${a[*]}"; do
for> echo $i
for> done
11
➜  ~ echo ${a[1]}
1
➜  ~ echo ${a[2]}
1
➜  ~ echo 'num of elemets='${#a[*]}
num of elemets=2

# it looks rather werid... so avoid using it...

194. Tranpose File

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

# Read from the file file.txt and print its transposed content to stdout.
awk '
{
    for(i = 1; i <= NF; ++i) {
        if(1 == NR) {
            s[i] = $i;
        }
        else {
            s[i] = s[i] " " $i 
        }
    }
}
END {
    for(i = 1; s[i] != ""; ++i) {
        print s[i];
    }
}' file.txt