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# 854.K-Similar-Strings

## 题目描述

Strings A and B are K-similar (for some non-negative integer K) if we can swap the positions of two letters in A exactly K times so that the resulting string equals B.
Given two anagrams A and B, return the smallest K for which A and B are K-similar.
Example 1:
Input: A = "ab", B = "ba"
Output: 1
Example 2:
Input: A = "abc", B = "bca"
Output: 2
Example 3:
Input: A = "abac", B = "baca"
Output: 2
Example 4:
Input: A = "aabc", B = "abca"
Output: 2
Note:
1 <= A.length == B.length <= 20
A and B contain only lowercase letters from the set {'a', 'b', 'c', 'd', 'e', 'f'}

## 代码

class Solution {
public int kSimilarity(String A, String B) {
Queue<String> queue = new ArrayDeque();
queue.offer(A);
Map<String, Integer> dist = new HashMap();
dist.put(A, 0);
while (!queue.isEmpty()) {
String S = queue.poll();
if (S.equals(B)) return dist.get(S);
for (String T : getNeighbors(S, B)) {
if (!dist.containsKey(T)) {
dist.put(T, dist.get(S) + 1);
queue.offer(T);
}
}
}
throw null;
}
public List<String> getNeighbors(String S, String target) {
List<String> ans = new ArrayList();
int i = 0;
for (; i < S.length(); i++) {
if (S.charAt(i) != target.charAt(i)) {
break;
}
}
char[] T = S.toCharArray();
for (int j = i + 1; j < S.length(); j++) {
if (S.charAt(j) == target.charAt(i)) {
swap(T, i, j);