Submission #43789

#	Time	Username	Problem	Language	Result	Execution time	Memory
43789		evpipis	구경하기 (JOI13_watching)	C++11	50 / 100	1069 ms	32400 KiB

watching

#include <bits/stdc++.h>
using namespace std;

const int len = 2e3+5, inf = 1e9;
int n, p, q, pp, qq, a[len];
int nex[2][len], pre[2][len], dp[len][len], best[len][len];

int finduse(int pos, int use1){
    if (pos == 0 && use1 == 0) return 0;
    if (pos == 0 && use1 != 0) return inf;
    if (best[pos][use1] != -1) return best[pos][use1];

    int ans = inf;
    if (use1 > 0)
        ans = min(ans, finduse(pre[0][pos], use1-1));
    ans = min(ans, finduse(pre[1][pos], use1)+1);

    return best[pos][use1] = ans;
}

int solve(int pos, int use1){
    if (pos == n+1) return 1;
    if (dp[pos][use1] != -1) return dp[pos][use1];

    int use2 = finduse(pos-1, use1), ans = 0;
    if (use1 < pp)
        ans = max(ans, solve(nex[0][pos], use1+1));
    if (use2 < qq)
        ans = max(ans, solve(nex[1][pos], use1));

    //if (hey) printf("pos = %d, use1 = %d, use2 = %d, ans = %d\n", pos, use1, use2, ans);
    return dp[pos][use1] = ans;
}

bool check(int w){
    for (int i = 1, j1 = 1, j2 = 1; i <= n; i++){
        while (j1 <= n && a[j1]-a[i]+1 <= w) j1++;
        while (j2 <= n && a[j2]-a[i]+1 <= 2*w) j2++;

        nex[0][i] = j1;
        nex[1][i] = j2;
    }

    for (int i = n, j1 = n, j2 = n; i >= 1; i--){
        while (j1 >= 1 && a[i]-a[j1]+1 <= w) j1--;
        while (j2 >= 1 && a[i]-a[j2]+1 <= 2*w) j2--;

        pre[0][i] = j1;
        pre[1][i] = j2;
    }

    qq = q, pp = p;
    if (q < p){
        swap(pp, qq);
        for (int i = 1; i <= n; i++){
            swap(nex[0][i], nex[1][i]);
            swap(pre[0][i], pre[1][i]);
        }
    }

    for (int i = 0; i <= n; i++)
        for (int j = 0; j <= pp; j++)
            dp[i][j] = best[i][j] = -1;

    return solve(1, 0);
}

int bs(){
    int l = 1, r = (inf+p+q)/(p+q), ans;
    while (l <= r){
        int mid = (l+r)/2;
        if (check(mid)){
            ans = mid;
            r = mid-1;
        }
        else
            l = mid+1;
    }

    return ans;
}

int main(){
    scanf("%d %d %d", &n, &p, &q);
    for (int i = 1; i <= n; i++)
        scanf("%d", &a[i]);
    sort(a+1, a+n+1);

    if (p+q >= n) printf("1\n");
    else printf("%d\n", bs());
    return 0;
}

Compilation message (stderr)

watching.cpp: In function 'int main()':
watching.cpp:84:34: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
     scanf("%d %d %d", &n, &p, &q);
                                  ^
watching.cpp:86:27: warning: ignoring return value of 'int scanf(const char*, ...)', declared with attribute warn_unused_result [-Wunused-result]
         scanf("%d", &a[i]);
                           ^
watching.cpp: In function 'int bs()':
watching.cpp:80:12: warning: 'ans' may be used uninitialized in this function [-Wmaybe-uninitialized]
     return ans;
            ^

• Subtask 1: 50 / 50
• Subtask 2: 0 / 50