二分查找

3道题解法类似，复杂度逐步提升。最长递增子序列：https://leetcode.cn/problems/longest-increasing-subsequence，俄罗斯套娃信封问题：https://leetcode.cn/problems/russian-doll-envelopes，删除元素后最大固定点数目：https://leetcode.cn/problems/maximize-fixed-points-after-deletions