Js源码
200. Number of Islands
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:
Input: grid = [ ["1","1","1","1","0"], ["1","1","0","1","0"], ["1","1","0","0","0"], ["0","0","0","0","0"] ] Output: 1 Example 2:
Input: grid = [ ["1","1","0","0","0"], ["1","1","0","0","0"], ["0","0","1","0","0"], ["0","0","0","1","1"] ] Output: 3
思考路程
1 深度遍历就可以，广度遍历也可以
127. Word Ladder
- Word Ladder
Given two words (beginWord and endWord), and a dictionary's word list, find the length of shortest transformation sequence from beginWord to endWord, such that:
Only one letter can be changed at a time. Each transformed word must exist in the word list. Note:
Return 0 if there is no such transformation sequence. All words have the same length. All words contain only lowercase alphabetic characters. You may assume no duplicates in the word list. You may assume beginWord and endWord are non-empty and are not the same. Example 1:
Input: beginWord = "hit", endWord = "cog", wordList = ["hot","dot","dog","lot","log","cog"]
Output: 5
Explanation: As one shortest transformation is "hit" -> "hot" -> "dot" -> "dog" -> "cog", return its length 5.
Example 2:
Input: beginWord = "hit" endWord = "cog" wordList = ["hot","dot","dog","lot","log"]
Output: 0
Explanation: The endWord "cog" is not in wordList, therefore no possible transformation.
思考过程
1 利用图，一个单词向下一个单词转换就是一条边，所以关键是构造出图，然后问题就转变为求最短路径的问题了。
126. Word Ladder II
Given two words (beginWord and endWord), and a dictionary's word list, find all shortest transformation sequence(s) from beginWord to endWord, such that:
Only one letter can be changed at a time Each transformed word must exist in the word list. Note that beginWord is not a transformed word. Note:
Return an empty list if there is no such transformation sequence. All words have the same length. All words contain only lowercase alphabetic characters. You may assume no duplicates in the word list. You may assume beginWord and endWord are non-empty and are not the same. Example 1:
Input: beginWord = "hit", endWord = "cog", wordList = ["hot","dot","dog","lot","log","cog"]
Output: [ ["hit","hot","dot","dog","cog"], ["hit","hot","lot","log","cog"] ] Example 2:
Input: beginWord = "hit" endWord = "cog" wordList = ["hot","dot","dog","lot","log"]
Output: []
Explanation: The endWord "cog" is not in wordList, therefore no possible transformation.
思考路程
1, 开始想根据127的思路，然后把宽度遍历，转成深度遍历，然后记录，但是有的测试遍历还是过不了。
473. Matchsticks to Square
Remember the story of Little Match Girl? By now, you know exactly what matchsticks the little match girl has, please find out a way you can make one square by using up all those matchsticks. You should not break any stick, but you can link them up, and each matchstick must be used exactly one time.
Your input will be several matchsticks the girl has, represented with their stick length. Your output will either be true or false, to represent whether you could make one square using all the matchsticks the little match girl has.
Example 1: Input: [1,1,2,2,2] Output: true
Explanation: You can form a square with length 2, one side of the square came two sticks with length 1. Example 2: Input: [3,3,3,3,4] Output: false
Explanation: You cannot find a way to form a square with all the matchsticks. Note: The length sum of the given matchsticks is in the range of 0 to 10^9. The length of the given matchstick array will not exceed 15.
思考路程
1 本来想排序，然后两两查找，发现这样不行，因为有可能四边形的一边是三个或者是四个
2 后来想到回溯法，类似于以前做过的题目，查找数组的子集
3 后来想到每个边，类似于一个桶，可以利用类似桶排序的原理
407. Trapping Rain Water II
Given an m x n matrix of positive integers representing the height of each unit cell in a 2D elevation map, compute the volume of water it is able to trap after raining.
Example:
Given the following 3x6 height map: [ [1,4,3,1,3,2], [3,2,1,3,2,4], [2,3,3,2,3,1] ]
Return 4. The above image represents the elevation map [[1,4,3,1,3,2],[3,2,1,3,2,4],[2,3,3,2,3,1]] before the rain.
After the rain, water is trapped between the blocks. The total volume of water trapped is 4.
Constraints:
1 <= m, n <= 110 0 <= heightMap[i][j] <= 20000
思考路程
1 刚开想着一行一列进行计算，发现根本解决不了
2 后来看了题解，才明白可以使用水漫金山来进行计算，一层层的来进行搜索。
