Date：2020/4/14
- 题目：https://leetcode-cn.com/problems/add-two-numbers-ii/ tip：利用栈模拟从后往前操作
- 题目：https://leetcode-cn.com/problems/sort-the-matrix-diagonally/ tip: 对角线遍历，然后利用set插入自动排序。则获取迭代器所指向的key是有序的。
- 题目：https://leetcode-cn.com/problems/sort-integers-by-the-power-value/ tip: 也是利用map中内部key是自动排序，所以依次遍历到对应位置即可（一定要清楚审题）
Date：2020/4/15
- 题目：https://leetcode-cn.com/problems/validate-stack-sequences/ tip：根据pop序列来倒推push序列是否可能
- 题目：https://leetcode-cn.com/problems/01-matrix/ tip：动态规划（四个方向） DFS和BFS（四个方向）可以多总结。
- 题目：https://leetcode-cn.com/problems/construct-binary-tree-from-inorder-and-postorder-traversal/ tip: 利用中序后序遍历序列的特点，进行递归构建。分好左右子树序列。
Date：2020/4/17
- https://leetcode-cn.com/problems/open-the-lock/ tip：双向BFS BFS模型
- 背包九讲（没咋看透 在加把油！！！）
Date: 2020/4/19
- https://leetcode-cn.com/problems/construct-binary-tree-from-preorder-and-inorder-traversal/ tip: 与中序和后序一样的思路
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https://leetcode-cn.com/problems/queens-that-can-attack-the-king/ tip:主要是构造八个方向的数组 思路不难
- https://leetcode-cn.com/problems/balance-a-binary-search-tree/submissions/ tip：我自己重建树，不过应该是AVL树的建立。
Date: 2020/4/20
- https://leetcode-cn.com/problems/number-of-islands/ tip：简单的DFS遍历
- https://leetcode-cn.com/problems/delete-leaves-with-a-given-value/ tip：设计到二叉树一般就是递归
- https://leetcode-cn.com/problems/the-k-th-lexicographical-string-of-all-happy-strings-of-length-n/ tip：简单回溯法
Date: 2020/4/21
1.https://leetcode-cn.com/problems/max-consecutive-ones-iii/ tip:滑动窗口
2.https://leetcode-cn.com/problems/minimum-size-subarray-sum/ tip:滑动窗口
3 https://leetcode-cn.com/problems/count-number-of-nice-subarrays/ tip:滑动窗口
Date: 2020/4/22
- https://leetcode-cn.com/problems/find-all-anagrams-in-a-string/ tip:滑动窗口
- https://leetcode-cn.com/problems/longest-substring-without-repeating-characters/ tip：滑动窗口
- https://leetcode-cn.com/problems/minimum-window-substring/ tip:滑动窗口
Date:2020/4/24
1 https://leetcode-cn.com/problems/shu-zu-zhong-de-ni-xu-dui-lcof/ tip：归并排序的应用 下同
2 https://leetcode-cn.com/problems/count-of-smaller-numbers-after-self/
3 https://leetcode-cn.com/problems/reverse-pairs/
Date：2020/4/25
1 https://leetcode-cn.com/problems/find-minimum-in-rotated-sorted-array-ii/ tip:二分 下同 不过细节挺多 卒
2 https://leetcode-cn.com/problems/search-in-rotated-sorted-array/
3 https://leetcode-cn.com/problems/search-in-rotated-sorted-array-ii/
4 https://leetcode-cn.com/problems/find-minimum-in-rotated-sorted-array/
Date：2020/4/28
1 https://leetcode-cn.com/problems/minimum-number-of-steps-to-make-two-strings-anagram/ Tip：map解决 也可以不用直接定义个char[26]更快
2 https://leetcode-cn.com/problems/lexicographical-numbers/ Tip:利用map内部自动排序，将数字转成字符串。厉害
3 https://leetcode-cn.com/problems/find-elements-in-a-contaminated-binary-tree/ Tip:二叉树 一般递归解决
Date：2020/4/29
1 https://leetcode-cn.com/problems/zai-pai-xu-shu-zu-zhong-cha-zhao-shu-zi-lcof/ Tip：两次二分
2 https://leetcode-cn.com/problems/find-in-mountain-array/ tip:二分查找分界点，然后在两个区域分别二分