题目：

题解：

func maxEnvelopes(envelopes [][]int) int {
    n := len(envelopes)
    if n == 0 {
        return 0
    }

    sort.Slice(envelopes, func(i, j int) bool {
        a, b := envelopes[i], envelopes[j]
        return a[0] < b[0] || a[0] == b[0] && a[1] > b[1]
    })

    f := make([]int, n)
    for i := range f {
        f[i] = 1
    }
    for i := 1; i < n; i++ {
        for j := 0; j < i; j++ {
            if envelopes[j][1] < envelopes[i][1] {
                f[i] = max(f[i], f[j]+1)
            }
        }
    }
    return max(f...)
}

func max(a ...int) int {
    res := a[0]
    for _, v := range a[1:] {
        if v > res {
            res = v
        }
    }
    return res
}