maxEnvelops

  public int maxEnvelopes(int[][] envelopes) {
        Arrays.sort(envelopes, (a, b) -> Integer.compare(a[0] * a[1], b[0] * b[1]));
        int n = envelopes.length;
        int[] lip = new int[n];
        int ans = Integer.MIN_VALUE;
        for (int i = 0; i < n; i++) {
            lip[i] = 1;
            for (int j = 0; j < i; j++) {
                if (envelopes[i][0] > envelopes[j][0] && envelopes[i][1] > envelopes[j][1]) {
                    lip[i] = Math.max(lip[i], 1 + lip[j]);
                }
            }
            ans = Math.max(ans, lip[i]);
        }
        return ans;
    }