05 August 2008
一个字符串中找到所有异位词子串的起始位置 - 滑动窗口 + HashMap/Array (模板集合，最后一个)
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class Solution {
public List<Integer> findAnagrams(String s, String t) {
List<Integer> result = new LinkedList<>();
if (t.length() > s.length()) {
return result;
}
Map<Character, Integer> map = new HashMap<>();
for (char c : t.toCharArray()) {
map.put(c, map.getOrDefault(c, 0) + 1);
}
int counter = map.size();
int begin = 0, end = 0;
// int head = 0;
// int len = Integer.MAX_VALUE;
while (end < s.length()) {
char c = s.charAt(end);
if (map.containsKey(c)) {
map.put(c, map.get(c) - 1);
if (map.get(c) == 0) {
counter--;
}
}
end++;
while (counter == 0) {
char tempc = s.charAt(begin);
if (map.containsKey(tempc)) {
map.put(tempc, map.get(tempc) + 1);
if (map.get(tempc) > 0) {
counter++;
}
}
if (end - begin == t.length()) {
result.add(begin);
}
begin++;
}
}
return result;
}
}
比较直接的每个字串检查，也能过，时间复杂度lenS * lenP
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class Solution {
public List<Integer> findAnagrams(String s, String p) {
List<Integer> result = new ArrayList<>();
if (s.isEmpty()) {
return result;
}
int lenS = s.length();
int lenP = p.length();
for (int i = 0; i < lenS - lenP + 1; i++) {
String temp = s.substring(i, i + lenP);
if (check(temp, p)) {
result.add(i);
}
}
return result;
}
private boolean check(String s1, String s2) {
int[] arr = new int[26];
int len = s1.length();
for (int i =0 ; i < len; i++) {
arr[s1.charAt(i) - 'a']++;
arr[s2.charAt(i) - 'a']--;
}
for (int ch : arr) {
if (ch != 0) {
return false;
}
}
return true;
}
}