題目
https://leetcode.com/problems/minimum-genetic-mutation/
題解
圖的 DFS，思路見(jiàn)草稿：
class Solution {int N;public int minMutation(String start
, String end
, String[] bank
) {HashSet<String> set
= new HashSet<>(Arrays.asList(bank
));bank
= set
.toArray(new String[0]);N = bank
.length
;Map<String, Set<String>> map
= new HashMap<>();for (int i
= 0; i
< N; i
++) {if (!map
.containsKey(bank
[i
])) {Set<String> i2j
= new HashSet<>();map
.put(bank
[i
], i2j
);}for (int j
= i
+ 1; j
< N; j
++) {if (!map
.containsKey(bank
[j
])) {Set<String> j2i
= new HashSet<>();map
.put(bank
[j
], j2i
);}if (mutate(bank
[i
], bank
[j
])) {map
.get(bank
[i
]).add(bank
[j
]);map
.get(bank
[j
]).add(bank
[i
]);}}}int min
= Integer.MAX_VALUE
;Set<String> visited
= new HashSet<>();for (String s
: bank
) { if (mutate(start
, s
)) {visited
.add(s
);int distance
= dfs(map
, s
, end
, visited
);if (distance
> 0) min
= Math.min(min
, distance
);visited
.remove(s
);}}return min
== Integer.MAX_VALUE
? -1 : min
;}public int dfs(Map<String, Set<String>> map
, String start
, String end
, Set<String> visited
) {if (visited
.size() == N) return start
.equals(end
) ? N : -1; if (start
.equals(end
)) return visited
.size();int min
= Integer.MAX_VALUE
;for (String k
: map
.get(start
)) {if (!visited
.contains(k
)) {visited
.add(k
);int distance
= dfs(map
, k
, end
, visited
);if (distance
> 0) min
= Math.min(min
, distance
);visited
.remove(k
);}}return min
;}public boolean mutate(String s1
, String s2
) {int diff
= 0;for (int i
= 0; i
< s1
.length(); i
++) {if (s1
.charAt(i
) != s2
.charAt(i
)) {if (++diff
> 1) return false;}}return true;}
}
總結(jié)
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