摘要：Design and implement a TwoSum class. It should support the following operations: add and find. add - Add the number to an internal data structure.find 阅读全文

摘要：Better idea is to maintain a hashset that contains at most k numbers 阅读全文

摘要：要注意一种情况：isUnique("cake"), 应该是true. 虽然他的缩写在afterabbr出现，但是那就是他自己，没有别的跟他一样 阅读全文

摘要：Graph, DFS (1) Build the map, the key is dividend, the value is also a map whose key is divisor and value is its parameter. For example, a / b = 2.0, 阅读全文

摘要：Given N axis-aligned rectangles where N > 0, determine if they all together form an exact cover of a rectangular region. Each rectangle is represented 阅读全文