hackerrank Diameter Minimization

#include<queue>
#include<cstdio>
#include<algorithm>
using namespace std;

int read_p,read_ca;
inline int read(){
    read_p=0;read_ca=getchar();
    while(read_ca<‘0‘||read_ca>‘9‘) read_ca=getchar();
    while(read_ca>=‘0‘&&read_ca<=‘9‘) read_p=read_p*10+read_ca-48,read_ca=getchar();
    return read_p;
}
queue <int> q;
int n,m,dis[1001],mmh=0;
inline int bfs(int x){
    int mmh=0,i,j,k;
    for (i=0;i<n;i++) dis[i]=1e9;dis[x]=0;
    q.push(x);
    while (!q.empty()) for (mmh=dis[k=q.front()],q.pop(),i=0;i<m;i++) if (j=(k*m+i)%n,dis[j]>dis[k]+1) dis[j]=dis[k]+1,q.push(j);
    return mmh;
}
int main(){
    register int i,j;
    n=read();m=read();
    for (i=0;i<n;i++) mmh=max(mmh,bfs(i));
    printf("%d\n",mmh);
    for (i=0;i<n;i++,puts(""))
    for (j=0;j<m;j++) printf("%d ",(i*m+j)%n);
}