Submission #1074369

#	Time	Username	Problem	Language	Result	Execution time	Memory
1074369		TheEpicCowOfLife	Mecho (IOI09_mecho)	C++14	100 / 100	219 ms	3360 KiB

mecho

#include <cstdio>
#include <queue>
#include <vector>
#include <algorithm>
#include <utility>
#include <cstring>
 
using namespace std;
 
typedef pair<int,int> pii;
 
bool is_g[805][805];
bool pushed[805][805];
 
bool bocc[805][805];
 
int sx, sy;
int fx, fy;
 
int n,s;
 
vector<pii> hv;
 
queue<pii> mq;
queue<pii> bq;
 
int ax[4] = {0,1,0,-1};
int ay[4] = {1,0,-1,0};
// can mecho make it back to the hive waiting k minutes?
bool decision(int k){
    queue<pii> mq;
    queue<pii> bq;
    memset(pushed, 0, sizeof(pushed));
    memset(bocc, 0, sizeof(bocc));
    mq.push({sx,sy});
    pushed[sx][sy] = true;
    for (pii cur : hv){
        bq.push(cur);
        bocc[cur.first][cur.second] = true;
    }
 
    for (int vi = 0; vi < k; vi++){
        int sz = bq.size();
        for (int i = 0 ; i < sz; i++){
            pii cur = bq.front();
            bq.pop();
            for (int j = 0; j < 4; j++){
                int cx = cur.first + ax[j];
                int cy = cur.second + ay[j];
                if (!bocc[cx][cy] && is_g[cx][cy]){
                    bocc[cx][cy] = true;
                    bq.push({cx,cy});
                }
            }
        }
    }
 
    while(true){
        int sz;
        for (int vi = 0; vi < s; vi++){
            sz = mq.size();
            for (int i = 0 ; i < sz; i++){
                pii cur = mq.front();
                mq.pop();
                if (bocc[cur.first][cur.second]) continue;
                for (int j = 0; j < 4; j++){
                    int cx = cur.first + ax[j];
                    int cy = cur.second + ay[j];
                    if (cx == fx && cy == fy) return true;
                    if (!bocc[cx][cy] && is_g[cx][cy] && !pushed[cx][cy]){
                        pushed[cx][cy] = true;
                        mq.push({cx,cy});
                    }
                }
            }
        }
        if (sz == 0) return false;
        sz = bq.size();
        for (int i = 0 ; i < sz; i++){
            pii cur = bq.front();
            bq.pop();
            for (int j = 0; j < 4; j++){
                int cx = cur.first + ax[j];
                int cy = cur.second + ay[j];
                if (!bocc[cx][cy] && is_g[cx][cy]){
                    bocc[cx][cy] = true;
                    bq.push({cx,cy});
                }
            }
        }
    }
 
}
 
int main(){
    scanf("%d %d", &n, &s);
    for (int y = 1; y <= n; y++){
        for (int x = 1; x <= n; x++){
            char inst;
            scanf(" %c", &inst);
            if (inst == 'G'){
                is_g[x][y] = true;
            }
            else if (inst == 'H'){
                hv.push_back({x,y});
            }
            else if (inst == 'M'){
                sx = x;
                sy = y;
                is_g[x][y] = true;
            }
            else if (inst == 'D'){
                fx = x;
                fy = y;
            }
        }
    }
 
    int best = -1;
    int lo = 0;
    int hi = n * n/2 + 1;
    while (lo <= hi){
        int mid = (lo + hi)/2;
        if (decision(mid)){
            lo = mid + 1;
            best = mid;
        }
        else{
            hi = mid - 1;
        }
    }
 
    printf("%d\n", best);
 
}

Compilation message (stderr)

mecho.cpp: In function 'int main()':
mecho.cpp:96:10: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
   96 |     scanf("%d %d", &n, &s);
      |     ~~~~~^~~~~~~~~~~~~~~~~
mecho.cpp:100:18: warning: ignoring return value of 'int scanf(const char*, ...)' declared with attribute 'warn_unused_result' [-Wunused-result]
  100 |             scanf(" %c", &inst);
      |             ~~~~~^~~~~~~~~~~~~~
mecho.cpp: In function 'bool decision(int)':
mecho.cpp:77:9: warning: 'sz' may be used uninitialized in this function [-Wmaybe-uninitialized]
   77 |         if (sz == 0) return false;
      |         ^~

• Subtask 1: 100 / 100