public class DayCode {    public static void main(String[] args) {        int[][] num = new int[][]{{5, 4}, {6, 4}, {6, 7}, {2, 3}};        int ans = new DayCode().maxEnvelopes(num);        System.out.println("ans is " + ans);    }
    /**     * https://leetcode-cn.com/problems/russian-doll-envelopes/submissions/     * @param envelopes     * @return     */    public int maxEnvelopes(int[][] envelopes) {        int ans = 0;        Arrays.sort(envelopes, new Comparator<int[]>() {            @Override            public int compare(int[] o1, int[] o2) {                if (o1[0] == o2[0]) {                    return o2[1] - o1[1];                } else {                    return o1[0] - o2[0];                }            }        });        int n = envelopes.length;        int[] heights = new int[n];        for (int i = 0; i < n; i++) {            heights[i] = envelopes[i][1];        }        ans = lengthOfLIS(heights);        return ans;    }
    /**     * https://leetcode-cn.com/problems/longest-increasing-subsequence/     * @param nums     * @return     */    public int lengthOfLIS(int[] nums) {        if (nums.length == 0) {            return 0;        }        int ans = 1;        int[] dp = new int[nums.length];        Arrays.fill(dp, 1);        for (int i = 1; i < nums.length; i++) {            for (int j = 0; j < i; j++) {                if (nums[i] > nums[j]) {                    dp[i] = Math.max(dp[i], dp[j] + 1);                }            }            ans = Math.max(dp[i], ans);        }        return ans;    }}