Problem #433: Minimum Genetic Mutation

Intuition & Strategy Breakdown

Use BFS starting from startGene. Mutate single characters to valid bank genes, tracking shortest mutation sequence distance.

Python Solution

def minMutation(startGene, endGene, bank):
    bankSet = set(bank)
    if endGene not in bankSet:
        return -1
    queue = [(startGene, 0)]
    visited = {startGene}
    while queue:
        current, dist = queue.pop(0)
        if current == endGene:
            return dist
        for i in range(8):
            for char in "ACGT":
                mutation = current[:i] + char + current[i+1:]
                if mutation in bankSet and mutation not in visited:
                    visited.add(mutation)
                    queue.append((mutation, dist + 1))
    return -1

Java Solution

class Solution {
    public int minMutation(String startGene, String endGene, String[] bank) {
        Set bankSet = new HashSet<>(Arrays.asList(bank));
        if (!bankSet.contains(endGene)) return -1;
        Queue> queue = new LinkedList<>();
        queue.add(new Pair<>(startGene, 0));
        Set visited = new HashSet<>();
        visited.add(startGene);
        char[] chars = {'A', 'C', 'G', 'T'};
        while (!queue.isEmpty()) {
            Pair currentPair = queue.poll();
            String current = currentPair.getKey();
            int dist = currentPair.getValue();
            if (current.equals(endGene)) return dist;
            for (int i = 0; i < 8; i++) {
                for (char c : chars) {
                    char[] mutationArr = current.toCharArray();
                    mutationArr[i] = c;
                    String mutation = new String(mutationArr);
                    if (bankSet.contains(mutation) && !visited.contains(mutation)) {
                        visited.add(mutation);
                        queue.add(new Pair<>(mutation, dist + 1));
                    }
                }
            }
        }
        return -1;
    }
}