naive string matching algorithm gone wrong

Question

I am trying to implement naive search and I do not get the expected result. Can anyone point out here, what could be the possible error.

function naive(string, str) {
    for (let i = 0; i <= string.length - str.length; i++) {
        if (string[i] == str[0]) {
            let counter = 1

            for (let j = 1; j <= str.length; j++) {
                if (string[i + j] == str[j]) {
                    counter++;
                    console.log(counter)
                } else
                    counter = 0;
            }

            if (counter == str.length) {
                console.log(`${counter} pattern matched at ${i}`)
            }
        } else
            console.log('nothing matched')
    }
}

Answer 1

var match_found = false;
function naive(string, str){
  for(let i =0; i <= string.length - str.length; i++){
      if(string[i] == str[0]){
        let counter= 1
            for(let j = 1; j < str.length; j++){
                if(string[i + j] == str[j]){    
                  counter++;
                }else{
                  break;
                }
            }
        if(counter == str.length){ 
          console.log('Pattern matched at ' + i);
          match_found = true;// can break; here if you wish to, else it will give you all matches present
        }
      }
  }
  if(match_found === false){
    console.log(str + ' not found in ' + string);
  }
}

naive('abcdgggabcdggg','ggg');

• You increment the counter when there is a match, but you need to break the loop where there is a mismatch.

• Your inner for loop condition needs to have j < str.length instead of j <= str.length, because index starts from 0.

• else console.log('nothing matched'). You can't just instantly decide that. If a string index doesn't match, you need to still keep looking for the rest of the indexes. Best way to go about it is to maintain a boolean flag for it as shown in the above code.