当操作对象是两个数的时候，优先考虑用其中一个数表示另一个数，减少变量个数,一般用到map存

涉及两个数的关系问题

flood fill && BFS

#include <iostream>
#include <algorithm>
#define x first
#define y second

using namespace std;
const int N = , M = N*N;
typedef pair<int,int> PII;

int n;
bool st[N][N];
char/int g[N][N];
PII q[M];

// 辐射式偏移
int dx[8] = {-1, -1, -1, 0, 1, 1, 1, 0};
int dy[8] = {-1, 0, 1, 1, 1, 0, -1, -1};

//上下左右偏移
int dx[4] = {-1, 0, 1, 0}, dy[4] = {0, 1, 0, -1};

//日字形偏移
int dx[8] = {-2, -1, 1, 2, 2, 1, -1, -2};
int dy[8] = {1, 2, 2, 1, -1, -2, -2, -1};

void bfs(int sx,int sy)
{
    int hh = 0, tt = 0;
    q[0] = {sx,sy};
    st[sx][sy] = true;

    while(hh <= tt)
    {
        auto t = q[hh ++];
        for(int i = 0 ; i < 8 ; i ++)
        {
            int a = t.x + dx[i];
            int b = t.y + dy[i];
            if(a < 0 || a >= n || b < 0 || b >= m) continue;//边界判断
            if(g[a][b] ... || st[a][b]) continue;//条件符合以及是否已经被遍历过的判断

            st[a][b] = true;//防止重复遍历
            q[++tt] = {a,b};//使得整个连通块全部被遍历完全
        }
    }
}

int main()
{
    cin >> n >> m;
    for(int i = 0 ; i < n ; i ++)
        for(int j = 0 ; j < m ; j ++)
            cin >> g[i][j];

    int cnt = 0;
    for(int i = 0 ; i < n ; i ++)
        for(int j = 0 ; j < m ; j ++)
        {
            if(g[i][j] ... && !st[i][j]) 
            {
                bfs(i,j);
                cnt ++;
            }
        }

    cout << cnt << endl;
    return 0;
}

DFS板子

#include <iostream>
#include <cstring>
#include <algorithm>

using namespace std;
const int N = 110;

int n,m;
int x1,y1,x2,y2;
char g[N][N];
bool st[N][N];
int dx[4] = {0,1,0,-1} , dy[4] = {1,0,-1,0}; 

bool dfs(int x,int y)
{
    if(x == x2 && y == y2) return true;

    st[x][y] = true;//内部dfs不需要恢复现场

    for (int i = 0; i < 4; i ++ )
    {
        int a = x + dx[i];
        int b = y + dy[i];

        if(a < 0 || a >= m || b < 0 || b >= m) continue;
        if(g[a][b] == '#') continue;
        if(st[a][b]) continue;

        if(dfs(a,b)) return true;
    }

    return false;
}
//当是多次查询时，记得重新memset一遍st数组为假


//dfsFLOOD FILL
int dfs(int x,int y)
{
    int num = 1;

    st[x][y] = true;//内部dfs不需要恢复现场

    for (int i = 0; i < 4; i ++ )
    {
        int a = x + dx[i];
        int b = y + dy[i];

        if(a < 0 || a >= n || b < 0 || b >= m) continue;
        if(g[a][b] == '#') continue;
        if(st[a][b]) continue;

        num += dfs(a,b);
    }

    return num;
}