354. Russian Doll Envelopes

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

        return len;
    }
}