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leetcode_java/src/main/java/LeetCodeJava/String/PalindromicSubstrings.java
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| Original file line number | Diff line number | Diff line change |
|---|---|---|
| @@ -0,0 +1,86 @@ | ||
| package LeetCodeJava.String; | ||
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| // https://leetcode.com/problems/palindromic-substrings/ | ||
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| public class PalindromicSubstrings { | ||
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| // V0 | ||
| // IDEA : BRUTE FORCE | ||
| // https://github.com/yennanliu/CS_basics/blob/master/leetcode_python/String/palindromic-substrings.py | ||
| public int countSubstrings(String s) { | ||
| int cnt = 0; | ||
| if (s == null || s.length() == 0){ | ||
| return cnt; | ||
| } | ||
| // two pointer | ||
| // a b c | ||
| // i | ||
| // j | ||
| // i as left pointer, j as right pointer | ||
| for (int i = 0; i < s.length(); i++){ | ||
| for (int j = i+1; j < s.length() + 1; j++){ | ||
| if (isPalindromic(s.substring(i, j))){ | ||
| cnt += 1; | ||
| } | ||
| } | ||
| } | ||
| return cnt; | ||
| } | ||
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| private boolean isPalindromic(String x){ | ||
| //System.out.println(x); | ||
| if (x.length() == 0){ | ||
| return true; | ||
| } | ||
| if (x.length() == 1){ | ||
| return true; | ||
| } | ||
| int l = 0; | ||
| int r = x.length()-1; | ||
| while (r >= l){ | ||
| if (x.charAt(l) != x.charAt(r)){ | ||
| return false; | ||
| } | ||
| r -= 1; | ||
| l += 1; | ||
| } | ||
| return true; | ||
| } | ||
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| // V1 | ||
| // https://leetcode.com/problems/palindromic-substrings/solutions/4705208/beats-100-easy-to-understand-c-java-python-solution/ | ||
| public int check(String s, int i, int j) { | ||
| int ans = 0; | ||
| while (i >= 0 && j < s.length() && s.charAt(i) == s.charAt(j)) { | ||
| ans++; | ||
| i--; | ||
| j++; | ||
| } | ||
| return ans; | ||
| } | ||
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| public int countSubstrings_1(String s) { | ||
| int ans = 0; | ||
| for (int i = 0; i < s.length(); i++) { | ||
| ans += check(s, i, i); | ||
| ans += check(s, i, i + 1); | ||
| } | ||
| return ans; | ||
| } | ||
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| // V2 | ||
| // https://leetcode.com/problems/palindromic-substrings/solutions/4667296/short-and-easy-method-3ms-please-upvote/ | ||
| public int solve(String s, int i, int j){ | ||
| if(i<0 || j==s.length()) return 0; | ||
| if(s.charAt(i) == s.charAt(j)) return solve(s, i-1, j+1) + 1; | ||
| else return 0; | ||
| } | ||
| public int countSubstrings_2(String s) { | ||
| int max = 0; | ||
| for(int i=0; i<s.length(); i++){ | ||
| max += solve(s,i,i) + solve(s,i,i+1); | ||
| } | ||
| return max; | ||
| } | ||
|
|
||
| } |
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