题目：

题解：

const L = 10
var bin = map[byte]int{'A': 0, 'C': 1, 'G': 2, 'T': 3}

func findRepeatedDnaSequences(s string) (ans []string) {
    n := len(s)
    if n <= L {
        return
    }
    x := 0
    for _, ch := range s[:L-1] {
        x = x<<2 | bin[byte(ch)]
    }
    cnt := map[int]int{}
    for i := 0; i <= n-L; i++ {
        x = (x<<2 | bin[s[i+L-1]]) & (1<<(L*2) - 1)
        cnt[x]++
        if cnt[x] == 2 {
            ans = append(ans, s[i:i+L])
        }
    }
    return ans
}