354. Russian Doll Envelopes

354. Russian Doll Envelopes

题目链接：https://leetcode.com/problems...

和300. Longest Increasing Subsequence类似的题，这里变成两个量了，依然是patient sort+binary search的思路。这里先按一个方向排序，另外一个方向按降序再排，这样就可以binary search了。

public class Solution {
    public int maxEnvelopes(int[][] envelopes) {
        if(envelopes.length == 0 || envelopes[0].length == 0) return 0;
        
        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+1];
        int idx = 0;
        for(int[] envelope : envelopes) {
            if(envelope[1] > dp[idx]) dp[++idx] = envelope[1];
            else if(envelope[1] <= dp[0]) dp[0] = envelope[1];
            else {
                int i = Arrays.binarySearch(dp, 0, idx+1, envelope[1]);
                if(i < 0) i = -(i + 1);
                dp[i] = envelope[1];
            }
        }
        
        return idx;
    }
}