_187_RepeatedDNASequences.java

package leetcode_1To300;

import java.util.ArrayList;
import java.util.HashSet;
import java.util.List;

/**
 * 本代码来自 Cspiration，由 @Cspiration 提供
 * 题目来源：http://leetcode.com
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 */
public class _187_RepeatedDNASequences {
    /**
     * 187. Repeated DNA Sequences
     * All DNA is composed of a series of nucleotides abbreviated as A, C, G, and T,
     * for example: "ACGAATTCCG". When studying DNA, it is sometimes useful to identify repeated sequences within the DNA.

     Write a function to find all the 10-letter-long sequences (substrings) that occur more than once in a DNA molecule.

     For example,

     Given s = "AAAAACCCCCAAAAACCCCCCAAAAAGGGTTT",

     Return:
     ["AAAAACCCCC", "CCCCCAAAAA"].

     time : O(n)
     space : O(n)

     * @param s
     * @return
     */
    public List<String> findRepeatedDnaSequences(String s) {
        HashSet<String> seen = new HashSet<>();
        HashSet<String> repeated = new HashSet<>();
        for (int i = 0; i < s.length() - 9; i++) {
            String temp = s.substring(i, i + 10);
            if (!seen.add(temp)) {
                repeated.add(temp);
            }
        }
        return new ArrayList<>(repeated);
    }
}