leetcode讲解--959. Regions Cut By Slashes

题目

In a N x N grid composed of 1 x 1 squares, each 1 x 1 square consists of a /, \, or blank space. These characters divide the square into contiguous regions.

(Note that backslash characters are escaped, so a \ is represented as "\\".)

Return the number of regions.

Example 1:

Input:
[
  " /",
  "/ "
]
Output: 2
Explanation: The 2x2 grid is as follows:

Example 2:

Input:
[
  " /",
  "  "
]
Output: 1
Explanation: The 2x2 grid is as follows:

Example 3:

Input:
[
  "\\/",
  "/\\"
]
Output: 4
Explanation: (Recall that because \ characters are escaped, "\\/" refers to \/, and "/\\" refers to /\.)
The 2x2 grid is as follows:

Example 4:

Input:
[
  "/\\",
  "\\/"
]
Output: 5
Explanation: (Recall that because \ characters are escaped, "/\\" refers to /\, and "\\/" refers to \/.)
The 2x2 grid is as follows:

Example 5:

Input:
[
  "//",
  "/ "
]
Output: 3
Explanation: The 2x2 grid is as follows:

Note:

• 1 <= grid.length == grid[0].length <= 30
• grid[i][j] is either '/', '\', or ' '.

题目地址

讲解

这道题是关于图的题，用到了并查集这个数据结构。好久没用并查集了，我主要是参考了这个博客:https://zxi.mytechroad.com/bl...

Java代码

class Solution {
    public int regionsBySlashes(String[] grid) {
        int result = 0;
        int index=-1;
        List<DisJointSet> list = new ArrayList<>();
        for(String s:grid){
            for(Character c:s.toCharArray()){
                for(int i=0;i<4;i++){
                    DisJointSet ds = new DisJointSet();
                    list.add(ds);
                }
            }
        }
        for(int j=0;j<grid.length;j++){
            for(int i=0;i<grid[j].length();i++){
                DisJointSet ds1 = list.get(++index);
                DisJointSet ds2 = list.get(++index);
                DisJointSet ds3 = list.get(++index);
                DisJointSet ds4 = list.get(++index);
                System.out.println(grid[j].charAt(i));
                if(grid[j].charAt(i)==' '){
                    DisJointSet.union(ds1, ds2);
                    DisJointSet.union(ds2, ds3);
                    DisJointSet.union(ds3, ds4);
                }
                if(grid[j].charAt(i)=='/'){
                    DisJointSet.union(ds1, ds4);
                    DisJointSet.union(ds2, ds3);
                }
                if(grid[j].charAt(i)=='\\'){
                    DisJointSet.union(ds1, ds2);
                    DisJointSet.union(ds3, ds4);
                }
                if(i<grid[j].length()-1){
                    DisJointSet.union(ds2, list.get(index+4));
                }
                if(j<grid.length-1){
                    DisJointSet.union(ds3, list.get(index+4*(grid[j].length()-1)+1));
                }
            }
        }
        for(DisJointSet ds:list){
            if(ds.find()==ds){
                result++;
            }
        }
        return result;
    }
}

class DisJointSet{
        public DisJointSet parent;
        public int rank;
        public DisJointSet(){
            rank = 0;
            parent = this;
        }
        public DisJointSet find(){
            if(parent!=this){
                parent = parent.find();
            }
            return parent;
        }
        public static void union(DisJointSet ds1, DisJointSet ds2){
            DisJointSet ds1Root = ds1.find();
            DisJointSet ds2Root = ds2.find();
            if(ds1Root!=ds2Root){
                if(ds1Root.rank>ds2Root.rank){
                    ds2Root.parent = ds1Root;
                }else if(ds1Root.rank<ds2Root.rank){
                    ds1Root.parent = ds2Root;
                }else if(ds1Root.rank==ds2Root.rank){
                    ds1Root.parent = ds2Root;
                    ds2Root.rank++;
                }
            }
        }
    }