摘要： 题目如下： Given a string S, count the number of distinct, non-empty subsequences of S . Since the result may be large, return the answer modulo 10^9 + 7. 阅读全文

摘要： 题目如下： In a given grid, each cell can have one of three values: the value 0 representing an empty cell; the value 1 representing a fresh orange; the va 阅读全文

摘要： 题目如下： In a binary tree, the root node is at depth 0, and children of each depth k node are at depth k+1. Two nodes of a binary tree are cousins if the 阅读全文