58. Lakes

flood fill

#include<stdio.h>
#include<stdlib.h>

#define N 410

int g[N][N], st[N][N];
int ans[N * N / 2 + 1], idx;
int qx[N * N], qy[N * N], hh, tt = -1;
int n, m;

int dx[] = {1, 0, -1, 0}, dy[] = {0, 1, 0, -1};

int cmp(const void *a, const void *b){
    return *(int*)a - *(int*)b;
}

int bfs(int x, int y){
    ++ tt;
    qx[tt] = x, qy[tt] = y;
    st[x][y] = 1;
    
    int start = hh;
    
    while(hh <= tt){
        int a = qx[hh], b = qy[hh];
        hh ++;
        
        for(int i = 0; i < 4; i ++){
            int nx = a + dx[i], ny = b + dy[i];
            if(nx < 0 || ny < 0 || nx >= n || ny >= m || g[nx][ny] == 0 || st[nx][ny]) continue;
            st[nx][ny] = 1;
            ++ tt;
            qx[tt] = nx, qy[tt] = ny;
        }
    }
    
    return tt - start + 1;
}

int main(){
    scanf("%d%d", &n, &m);
    
    for(int i = 0; i < n; i ++)
        for(int j = 0; j < m; j ++)
            scanf("%d", &g[i][j]);
            
    for(int i = 0; i < n; i ++)
        for(int j = 0; j < m; j ++)
            if(g[i][j] && !st[i][j]){
                int res = bfs(i, j);
                if(res) ans[idx ++] = res;
            }
    
    qsort(ans, idx, sizeof(int), cmp);
    
    for(int i = idx - 1; i >= 0; i --) printf("%d
", ans[i]);
    
    return 0;
}