• This is a summary of Tree Problems in LeetCode. Including the thought, code and some tricks.

Preorder

100. Same Tree

• 可套用模板，双pre

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  public boolean isSameTree(TreeNode p, TreeNode q) { if(p == null && q == null) return true; if(p == null || q == null) return false; if(p.val != q.val) return false; return isSameTree(p.left, q.left) && isSameTree(p.right, q.right); }

大佬总结链接)
核心模板

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public List<List<Integer>> subsetsWithDup(int[] nums) {
    List<List<Integer>> res = new ArrayList<>();
    if (nums.length == 0) return res;
    Arrays.sort(nums);//排序很关键
    helper(res, new ArrayList<>(), nums, 0);
    return res;
}

//有些需要start，有些不需要
private void backtrack(List<List<Integer>> res, List<Integer> temp, int[] nums, int start){
    if (满足条件){
        res.add(new ArrayList<>(temp));
        return;
    }
    for (int i = start; i < nums.length; i++){//构建循环
        //1. 是否去重
        //2. temp添加元素
        //3. 递归调用，param变化
        //4. temp去掉末尾元素
    }
}

DBMS Exam2 Review

Structured Query Language (SQL) - Lecture 11

SQL is the standard relational database language and is related to the tuple relational calculus.
Standard enables easier switch to other DBMS, queries remain unchanged.

Main objectives

• Create the database and relation structures
• Perform basic data management tasks, such as insertion, modification, and deletion of data from the relations
• Perform both simple and complex queries
• Be portable between different DBMS
• Perform the aforementioned services with minimal user efforts
• Perform the aforementioned services with maximum performance
  Read more »