dfs,bfs,UnionFind,slide window模版java

dfs图的连通分量

// dfs
class Solution {
    //图的连通分量
    boolean[] visit;
    public int mainDfs(int[][] M) {
        int n = M.length;
        if(n <= 0) return 0;
        visit = new boolean[n];
        int cnt = 0;
        for(int i = 0;i < n;i++){
            if(!visit[i]){
                dfs(M,i);
                cnt++;
            }
        }
        return cnt;
    }
    private void dfs(int[][] M,int i){
        visit[i] = true;
        for(int j = 0;j < M.length;j++){
            if(!visit[j] && M[i][j] == 1)
                dfs(M,j);
        }
    }
}

dfs非图关系，而是水平垂直方向连通

class Solution {
    boolean[][] visit;
    int[] dx = {0,-1,0,1},dy = {-1,0,1,0};
    int cnt = 0;
    public int maindfs(char[][] grid) {
         if(grid == null || grid.length==0 || grid[0].length==0)  return 0;
         visit = new boolean[grid.length][grid[0].length];
         for(int i = 0;i < grid.length;i++){
             for(int j = 0;j < grid[0].length;j++){
                 if(!visit[i][j] && grid[i][j] == '1'){
                     cnt++;
                     dfs(grid,i,j);
                 }
             }    
         }    
        return cnt;
    }
    private void dfs(char[][] grid,int i,int j ){
        //if(i < 0 || i >= grid.length || j < 0 || j >= grid[0].length)  return;
        visit[i][j] = true;
        for(int k = 0;k < 4;k++){
            int newI = i + dx[k],newJ = j + dy[k];
            if(isValid(grid,newI,newJ) && !visit[newI][newJ])  dfs(grid,newI,newJ);
        }
    }
    private boolean isValid(char[][] grid,int i,int j){
         if(i < 0 || i >= grid.length || j < 0 || j >= grid[0].length || grid[i][j] == '0')  
            return false;
         return true;
    }
}

bfs

//入参简写，为图，源节点以及v为处理你的需求
public void bfs(Graph,s,v){
	v(s);
	visited[s] = true;  //记录是否访问过
	q.add(s);
	while(queue非空){
	  v = q.poll();
	  for(i:v的临边){
	     if(!visited[i]){
	     	visited[i] = true;
	     	visit(i);
	     	q.add(i);
	     }
	  }
  }
}

UnionFind

    class UnionFind{
        public int[] parent;
        public UnionFind(int n){
            parent = new int[n];
            //数组初始化
            for(int i = 0;i < n;i++)
                parent[i] = i;
        }
        public void union(int i,int j){
             i = find(i);
             j = find(j);
             //一下根据你的需求，谁连接谁
             if(i < j) parent[j] = i;
             else      parent[i] = j;
        }
        public int find(int x){
            while(x != parent[x]) x = parent[x];
            return x;
        }
    }

 public List<Integer> findAnagrams(String s, String p) {
        Map<Character,Integer> map = new HashMap<>();
        for(char c: p.toCharArray())  map.put(c,map.getOrDefault(c,0)+1);//初始化map
        int cnt = map.size();
        int begin = 0,end = 0;
        ArrayList<Integer> res = new ArrayList<>();
        while(end < s.length()){
            char c = s.charAt(end);
            if(map.get(c) != null){       //减计数
                 map.put(c,map.get(c) - 1);
                 if(map.get(c) == 0)  cnt--;
            } 
            end++;
            while(cnt == 0){
                if(end - begin == p.length())   //处理结果
                    res.add(begin);
                char tmp = s.charAt(begin);
                if(map.get(tmp) != null){  //加计数
                    map.put(tmp,map.get(tmp)+1);
                    if(map.get(tmp) > 0)  cnt++;
                }
                begin++;
            }
            
        }
        return res;
    }