# Problem:

https://leetcode.com/problems/next-closest-time/description/
no limit on how many times a digit can be reused.

You may assume the given input string is always valid. For example, “01:34”, “12:09” are all valid. “1:34”, “12:9” are all invalid.

## Example 1:

Input: "19:34"
Output: "19:39"
Explanation: The next closest time choosing from digits 1, 9, 3, 4, is 19:39,
which occurs 5 minutes later.
It is not 19:33, because this occurs 23 hours and 59 minutes later.


## Example 2:

Input: "23:59"
Output: "22:22"
Explanation: The next closest time choosing from digits 2, 3, 5, 9, is 22:22.
It may be assumed that the returned time is next day's time since it is smaller
than the input time numerically.

# Related Problems:

Problem:

Given a 2d grid map of '1's (land) and '0's (water), count the number of islands. An island is surrounded by water and is formed by connecting adjacent lands horizontally or vertically. You may assume all four edges of the grid are all surrounded by water.

Example 1:

Example 2:

# Idea: DFS

Use DFS to find a connected component (an island) and mark all the nodes to 0.

Time complexity: O(mn)

Space complexity: O(mn)

# Related Problems

Problem:

Given a non-empty string s, you may delete at most one character. Judge whether you can make it a palindrome.

Example 1:

Example 2:

Note:

1. The string will only contain lowercase characters a-z. The maximum length of the string is 50000.

Idea:

Greedy, delete the first unmatched char

Time complexity

O(n)

Solution:

# Problem:

Given two binary trees, write a function to check if they are the same or not.

Two binary trees are considered the same if they are structurally identical and the nodes have the same value.

## Example 1:

Input:     1         1
/ \       / \
2   3     2   3

[1,2,3],   [1,2,3]

Output: true


## Example 2:

Input:     1         1
/           \
2             2

[1,2],     [1,null,2]

Output: false


## Example 3:

Input:     1         1
/ \       / \
2   1     1   2

[1,2,1],   [1,1,2]

Output: false


# Solution: Recursion

Time complexity: O(n)

Space complexity: O(n)