leetcode- Minimum Cost to Convert String I

/**
 * @param {string} source
 * @param {string} target
 * @param {character[]} original
 * @param {character[]} changed
 * @param {number[]} cost
 * @return {number}
 */
var minimumCost = function(source, target, original, changed, cost) {
    const getNumber = (char) => char.charCodeAt() - 97;

    const graph = Array.from({length:26}, (el,idx1) => Array.from({length:26}, (el,idx2) => idx1===idx2? 0:Infinity));

    for(let idx = 0; idx < original.length; idx++){
        const u = getNumber(original[idx]);
        const v = getNumber(changed[idx]);
        const uvCost = cost[idx];

        graph[u][v] = Math.min(graph[u][v], cost[idx]);
    }

    for(let w = 0; w < 26; w++){
        for(let u = 0; u < 26; u++){
            for(let v = 0; v < 26; v++){
                if(graph[u][w] + graph[w][v] < graph[u][v]){
                    graph[u][v] = graph[u][w] + graph[w][v];
                }
            }
        }
    }
    
    let totalCost = 0;
    for(let idx = 0; idx < source.length; idx++){
        const u = getNumber(source[idx]);
        const v = getNumber(target[idx]);
        totalCost += graph[u][v];

        if(totalCost === Infinity) return -1;
    }

    return totalCost;
};