substring-with-concatenation-of-all-words.js

/**
 * @param {string} s
 * @param {string[]} words
 * @return {number[]}
 */

var findSubstring = function(s, words) {

    // Resultant list
    const indices = [];
    
    // Base conditions
    if (s === null || s.length === 0 || words === null || words.length == 0) {
        return indices;
    }
    
    // Store the words and their counts in a hash map
    const wordCount = words.reduce((a, b) => {
        a[b] = (a[b] + 1) || 1;
        return a;
    }, {});
    
    // Length of each word in the words array
    const wordLength = words[0].length;
    
    // Length of all the words combined in the array
    const wordArrayLength = wordLength * words.length;
    
    // Loop for the entire string
    for (let i = 0; i <= s.length - wordArrayLength; i++) {
    
        // Get the substring of length equal to wordArrayLength
        let current = s.substring(i, i + wordArrayLength);
        
        // Map to store each word of the substring
        const wordMap = {};
        
        // Index to loop through the words array
        let index = 0;
        
        // Index to get each word in the current
        let j = 0;
        
        // Loop through each word of the words array
        while (index < words.length) {
            
            // Divide the current string into strings of length of
            // each word in the array
            const part = current.substring(j, j + wordLength);
            
            // Put this string into the wordMap
            wordMap[part] = (wordMap[part] + 1) || 1;
            
            // Update j and index
            j += wordLength;
            index++;
        }
        
        // At this point compare the maps
        
        let a = JSON.stringify(Object.entries(wordCount).sort());
        let b = JSON.stringify(Object.entries(wordMap).sort());
        if (a === b) {
            indices.push(i);
        }
    }
    
    return indices;  
    
};