lower_bound、upper_bound、binary_search、equal_range | STL

本章覆盖：sorted / partitioned precondition；`lower_bound`；`upper_bound`；`binary_search`；`equal_range`；logarithmic comparisons；iterator traversal complexity；random access vs forward iterator；member lower_bound in map/set；comparator consistency；LeetCode / 秋招高频。