ccc-2019.sh

ccc-2019.sh

#!/bin/bash

# Storing the input string
pattern=$1
string=$2

# We will use 2 pointers
ptrPattern=0
ptrString=0

# Getting the lenght of pattern and string
lenPattern=${#pattern}
lenString=${#string}

# Stop pointer navigation when we reach end of string or pattern
while [ $ptrPattern -lt $lenPattern ] && [ $ptrString -lt $lenString ];
do

    matching= false
    # if characters at the 2 pointers are matching , or if the current pattern is '.' it's a match
    if [ ${pattern:ptrPattern:1} == '.' ] || [ ${pattern:ptrPattern:1} == ${string:ptrString:1} ]
     then matching=true
     else matching=false
    fi

    # We increase the pattern pointer by +1 
    # Yes there is an abuse of bash as we could overflow `${pattern:ptrPattern:1}`, it won't break
    # In other language a test to check if we are off limit would be needed
    let ptrPattern++
    
    # Treating the special character '*'
    if [[ ${pattern:ptrPattern:1} == "*" ]]
    then 
            # If there was a match, we add +1 to the string pointer to test on the next loop the next character 
            # But we -1 the pattern matching as we don't know if the sequence has been finished
            if $matching 
            then
                let ptrPattern--
                let ptrString++
            else # we arrive a the end of a `x*` pattern, as it can be 0 character valid, we just need to check the next pattern character with the current string character
                let ptrPattern++
                  
            fi
    else # Next pattern character is as character or `.`
        if $matching  # If it matches, we can move to next string character
        then
            let ptrString++
        else  #If it didn't match, the string doesn't match the pattern, we can `exit 1` to notify error
            exit 1
        fi
    fi
done

# As '.' is wildcard for any character, the program will always be "blocked" in case of a '.*' 
# So we need the extra step here in case there is a ".*" at the end of the pattern
if [[ ${pattern:ptrPattern:1} == '.' ]]
then 
    let ptrPattern+=2
fi

# Check that we arrive at the end of both string, if not its not matching
exit $([ $ptrPattern -ge $lenPattern ] && [ $ptrString -ge $lenString ])