Loading problem…
A gene string can be represented by an 8-character long string, with choices from 'A', 'C', 'G', and 'T'. Suppose we need to investigate a mutation from a gene string startGene to a gene string endGene where one mutation is defined as one single character changed in the gene string. - For example, "AACCGGTT" --> "AACCGGTA" is one mutation. There is also a gene bank that records all the valid gene mutations. A gene must be in bank to make it a valid gene string. Given the two gene strings startGene and endGene and the gene bank bank, return the minimum number of mutations needed to mutate from startGene to endGene. If there is no such a mutation, return -1. Note that the starting point is assumed to be valid, so it might not be included in the bank.
Example 1
Input: startGene = AACCGGTT, endGene = AAACGGTA, bank = ["AACCGGTA","AACCGCTA","AAACGGTA"]
Output: 2
Explanation: Change the last character to get AACCGGTA, which is in the bank. Then change the third character to get AAACGGTA, the target. That is 2 mutations.
Example 2
Input: startGene = AACCGGTT, endGene = AACCGGTA, bank = ["AACCGGTA"]
Output: 1
Explanation: Changing only the last character turns AACCGGTT into AACCGGTA, which is in the bank and is the target.
Example 3
Input: startGene = AAAAACCC, endGene = AACCCCCC, bank = ["AAAACCCC","AAACCCCC","AACCCCCC"]
Output: 3
Explanation: Each step turns one more 'A' into 'C': AAAAACCC → AAAACCCC → AAACCCCC → AACCCCCC. Each intermediate gene is in the bank, so 3 mutations are needed.
Each valid gene is a graph node; two genes are connected if they differ by exactly one character. The minimum number of mutations is the shortest path from startGene to endGene, which BFS finds level by level.
Run checks all cases above. Submit evaluates all test cases.