DFS深度优先搜索
对称二叉树(+++++)
力扣第101题: https://leetcode-cn.com/problems/symmetric-tree/
二叉树的最大深度(+++)
力扣第104题: https://leetcode-cn.com/problems/maximum-depth-of-binary-tree/
从前序与中序遍历序列构造二叉树(++)
力扣第105题: https://leetcode-cn.com/problems/construct-binary-tree-from-preorder-and-inorder-traversal/
从中序与后序遍历序列构造二叉树(++)
力扣第106题: https://leetcode-cn.com/problems/construct-binary-tree-from-inorder-and-postorder-traversal/
将有序数组转换为二叉搜索树(++++)
力扣第108题: https://leetcode-cn.com/problems/convert-sorted-array-to-binary-search-tree/
岛屿数量(++)
力扣第200题: https://leetcode-cn.com/problems/number-of-islands/
课程表 (+)
力扣第207题: https://leetcode-cn.com/problems/course-schedule/
课程表 II (+)
力扣第210题: https://leetcode-cn.com/problems/course-schedule-ii/
字符串解码 (++)
力扣第394题: https://leetcode-cn.com/problems/decode-string/
扁平化多级双向链表 (+)
力扣第430题: https://leetcode-cn.com/problems/flatten-a-multilevel-doubly-linked-list/
01 矩阵 (+)
力扣第542题: https://leetcode-cn.com/problems/01-matrix/
岛屿的最大面积 (++)
力扣第695题: https://leetcode-cn.com/problems/max-area-of-island/