354. 俄罗斯套娃信封问题

3, 组合为: 

class Solution:
    def maxEnvelopes(self, envelopes: List[List[int]]) -> int:
        if not envelopes:
            return 0
        envelopes.sort(key=lambda x: (x[0], -x[1]))
        nums = [x[1] for x in envelopes]
        n = len(nums)
        dp = [1] * n
        res = 1
        for i in range(1, n):
            for j in range(i):
                if nums[j] < nums[i]:
                    dp[i] = max(dp[i], dp[j] + 1)
            res = max(res, dp[i])
        return res

class Solution {
    public int maxEnvelopes(int[][] envelopes) {
        int n;
        if (envelopes == null || (n = envelopes.length) == 0) return 0;
        Arrays.sort(envelopes, (a, b) -> {
            return a[0] == b[0] ? b[1] - a[1] : a[0] - b[0];
        });
        int[] dp = new int[n];
        Arrays.fill(dp, 1);
        int res = 1;
        for (int i = 1; i < n; ++i) {
            for (int j = 0; j < i; ++j) {
                if (envelopes[j][1] < envelopes[i][1]) {
                    dp[i] = Math.max(dp[i], dp[j] + 1);
                }
            }
            res = Math.max(res, dp[i]);
        }
        return res;
    }
}