一道简单的染色题(需要排序)

https://www.luogu.org/problemnew/show/P2919

#include <bits/stdc++.h>
#define read read()
#define up(i,l,r) for(int i = l; i<= r; i++)
using namespace std;
const int N = 705;
struct point{
    int x,y,h;
}p[N * N];

int read
{
    int x = 0;char ch = getchar();
    while(ch < 48 || ch > 57) ch = getchar();
    while(ch >=48 && ch <= 57) {x = 10 * x + ch - 48; ch = getchar();}
    return x; 
}

bool cmp(point a,point b) {return a.h > b.h;}

int n,m,vis[N][N],ans,height[N][N];
int dx[] = {0,-1,-1,-1, 0, 0, 1, 1, 1};
int dy[] = {0,-1, 0, 1,-1, 1,-1, 0, 1}; 

void dfs(int x,int y)
{
    up(i,1,8)
    {
        int nx = dx[i] + x, ny = dy[i] + y;
        if(vis[nx][ny] || height[nx][ny] > height[x][y]) continue; 
        if( nx <= 0 || ny <= 0 || nx > n || ny > m ) continue;
        vis[nx][ny] = 1,dfs(nx,ny);
    }
}

int main()
{
    n = read; m = read;
    int cnt = 0;
    up(i,1,n) up(j,1,m)
    {
        p[++cnt].x = i;
        p[cnt].y = j;
        p[cnt].h = read;
        height[i][j] = p[cnt].h;
    }
    sort(p + 1,p + cnt + 1,cmp);
    up(i,1,cnt)
    {
        if(!vis[p[i].x][p[i].y])
        {
            vis[p[i].x][p[i].y] = 1;
            dfs(p[i].x,p[i].y);//染色 
            ans++;
        }
    }
    printf("%d",ans);
    return 0;
}