摘要：
Given a binary tree, find its minimum depth. The minimum depth is the number of nodes along the shortest path from the root node down to the nearest l 阅读全文
摘要：
Given a binary tree, determine if it is height-balanced. For this problem, a height-balanced binary tree is defined as a binary tree in which the dept 阅读全文
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1、#{}： #{}解析为一个 JDBC 预编译语句（prepared statement）的参数标记符，就像JDBC中使用Statement进行数据库操作，sql语句直接与参数值拼接，容易引发sql注入攻击。 2、${}: ${仅仅为一个纯碎的 string 替换，在动态 SQL 解析阶段将会进行 阅读全文
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1、内存泄漏定义 sun官方解释：Another common problem with explicit memory management is space leaks. These leaks occur when memory is allocated and no longer refer 阅读全文