JavaScript Program to Check if String Follows Order of Characters Defined by a Pattern or Not

In this JavaScript article, we will see the solution to the problem of checking if a string follows the order of characters defined by a pattern or not. We have given a string and pattern as the input and our task is to develop a program that will check whether the input string follows the same pattern according to the pattern given.

Example:

To solve this problem, we have three different approaches which are mentioned below:

• Using Loops in JavaScript
• Using Map in JavaScript
• Using Builtin Functions ‘every’, ‘reduce’, and ‘split’ in JavaScript

Using JavaScript Loops

• In this apporach, we are using the looping in JavaScript, where we are comparing the order of the chatacter occurences between the input pattern and the input string.
• We are iterating thorugh them, and also having a track of max and min indexes of he chatacter occurences.
• If the patterm’s characters order is matched in the input string’s order then the true result is returned else the false result will be returned.

Examples:

Javascript

function checkPattern(str, pattern) {

    // lcmi -> Last char max index
    // ccmi -> current char max index
    // ccmin -> current char min index
    let lcmi = -1, ccmi = -1, ccmin = -1;
    let matchValue = true;
    lcmi = lastOcc(str, pattern[0]);
    for (i = 1; i < pattern.length; i++) {
        ccmi = lastOcc(str, pattern[i]);
        ccmin = firstOcc(str, pattern[i]);
        if (lcmi < ccmi && lcmi < ccmin) {
            matchValue = true;
        }
        else {
            matchValue = false;
        }
        lcmi = ccmi;
        if (matchValue == false)
            break;
    }
    return matchValue;
}
function lastOcc(str, chr) {
    let currentIdx = 99999999, maxIdx = -1;
    for (j = 0; j < str.length; j++) {
        if (chr == str[j]) {
            currentIdx = j;
            if (currentIdx > maxIdx)
                maxIdx = currentIdx;
        }
    }
    return maxIdx;
}
function firstOcc(str, chr) {
    let currentIdx = 99999999, minIndex = 999999999;
    for (k = 0; k < str.length; k++) {
        if (chr == str[k]) {
            currentIdx = k;
            if (currentIdx < minIndex)
                minIndex = currentIdx;
        }
    }
    return minIndex;
}
console.log(checkPattern("engineers rock", "er"));
console.log(checkPattern("engineers rock", "egr"));
console.log(checkPattern("engineers rock", "gsr"));

Output

true
false
false

Using JavaScript Map

• In this apporch, we are using the Maps in JavaScript where we have used the two map objects (map1 and map2).
• This objects establish the connection between the chacraters in the input pattern and words in the input string, as well as the reverse mapping.
• This assures that the mappings are proper and returns true if the character and words are aligned correctly else false will be returned.

Examples:

Javascript

function checkPattern(str, pattern) {
    let words = str.split(' ')
    if (pattern.length !== words.length) return false
    let map1 = new Map();
    let map2 = new Map();
    for (let i = 0; i < pattern.length; i++) {
        let key = pattern[i];
        let value = words[i];
        if (map1.has(key) || map2.has(value)) {
            if (map1.get(key) !== value) return false;
            if (map2.get(value) !== key) return false;
        } else {
            map1.set(key, value);
            map2.set(value, key);
        }
    }
    return true;
};

console.log(checkPattern("engineers rock", "er"));
console.log(checkPattern("engineers rock", "egr"));
console.log(checkPattern("engineers rock", "gsr"));

Output

true
false
false

Using Builtin Functions ‘every‘, ‘reduce‘, and ‘split‘

• In this apporach we are using inbuilt fucntions rather than using complex data structures.
• We firslty split the input string into words and then by using reduce funtion we create a mapping between pattern chatacters and the corresposnding words.
• Lastly, we check if all the mapped values are aligned properly witht he words in the input string using the every function.
• If they are aligned properly then true result will be returned else false result will be returned.

Example:

Javascript

function checkPattern(str, pattern) {
    let words = str.split(" ");
    if (words.length !== pattern.length) {
        return false;
    }

    let patternToWord = pattern.split("").reduce((map, character, index) => {
        if (!map.has(character)) {
            map.set(character, words[index]);
        } else if (map.get(character) !== words[index]) {
            return false;
        }
        return map;
    }, new Map());
    let values = [...patternToWord.values()];
    let ans = values.every((value, index) => value === words[index]);

    return ans;
}

console.log(checkPattern("engineers rock", "er"));
console.log(checkPattern("engineers rock", "egr"));
console.log(checkPattern("engineers rock", "gsr"));

Output

true
false
false