Codeforces #417(Div 2)

B. Sagheer, the Hausmeister

dp&分类讨论

#include <bits/stdc++.h>
using namespace std;
int n, m;
char str[17][305];
int lft[17], rgt[17];
int dp[17][2];
int main()
{
    memset(dp, -1, sizeof dp);
    scanf("%d%d", &n, &m), m += 2;
    int beg = -1;
    for (int i = 1; i <= n; i++) {
        scanf("%s", str[i]+1);
        lft[i] = rgt[i] = -1;
        for (int j = 1; j <= m; j++) {
            if (lft[i] == -1 && str[i][j] == '1') lft[i] = j;
            if ( str[i][j] == '1') rgt[i] = j;
        }
        if (lft[i] != -1) beg = 1;
        //cout << lft[i] << " " << rgt[i] << endl;
    }
    int bg = 1;
    while (lft[bg] == -1 && bg <= n) bg++;
    if (bg > n) { puts("0"); return 0; } 
    dp[bg][0] = rgt[bg]-1, dp[bg][1] = m-lft[bg];
    // cout << dp[1][0] << " " << dp[1][1] << endl;
    for (int i = bg+1; i <= n; i++) {
        for (int j = 0; j <= 1; j++) {
            dp[i][j] = 23333333;
            int adi = 0;
            if (lft[i] == -1) adi = 0;
            else if (j == 0) adi = (rgt[i]-1)*2;
            else adi = (m-lft[i])*2;
            for (int k = 0; k <= 1; k++) {
                if (j != k) dp[i][j] = min(dp[i][j], dp[i-1][k]+m);
                else dp[i][j] = min(dp[i][j], dp[i-1][k]+adi+1);
            }
            // cout << dp[i][j] << " ";
        }
        // cout << endl;
    }
    cout << dp[n][0] << endl;
    return 0;
}

C. Sagheer and Nubian Market

二分/枚举k，然后排序...

#include <bits/stdc++.h>
using namespace std;
const int MAXN = 100005;
int A[MAXN], C[MAXN], n, S;
int main()
{
    scanf("%d%d", &n, &S);
    for (int i = 1; i <= n; i++)
        scanf("%d", &A[i]);
    int ans = 0, ct = INT_MAX;
    for (int k = 1; (long long)k*(k+1)*k/2 <= S && k <= n; k++) {
        for (int i = 1; i <= n; i++) {
            if (A[i]+1ll*i*k <= S)
                C[i] = A[i]+i*k;
            else C[i] = S+1;
        }
        sort(C+1, C+n+1);
        int cnt = 0, mon = 0, i = 1;
        while (cnt < k && mon+C[i] <= S && i <= n) 
            mon += C[i], cnt++, i++;
        if (cnt == k) {
            if (cnt > ans) 
                ans = cnt, ct = mon;
            else if (cnt == ans)
                ct = min(ct, mon);
        }
    }
    if (ans == 0) { printf("0 0"); }
    else printf("%d %d\n", ans, ct);
    return 0;
}

E. Sagheer and Apple Tree

阶梯博弈...只有（从叶子算第一层起）奇数层有影响。分类讨论换奇数/奇数，奇数/偶数和偶数/偶数。

#include <bits/stdc++.h>
using namespace std;
const int MAXN = 100005;
int A[MAXN], C[MAXN], n, S;
int main()
{
    scanf("%d%d", &n, &S);
    for (int i = 1; i <= n; i++)
        scanf("%d", &A[i]);
    int ans = 0, ct = INT_MAX;
    for (int k = 1; (long long)k*(k+1)*k/2 <= S && k <= n; k++) {
        for (int i = 1; i <= n; i++) {
            if (A[i]+1ll*i*k <= S)
                C[i] = A[i]+i*k;
            else C[i] = S+1;
        }
        sort(C+1, C+n+1);
        int cnt = 0, mon = 0, i = 1;
        while (cnt < k && mon+C[i] <= S && i <= n) 
            mon += C[i], cnt++, i++;
        if (cnt == k) {
            if (cnt > ans) 
                ans = cnt, ct = mon;
            else if (cnt == ans)
                ct = min(ct, mon);
        }
    }
    if (ans == 0) { printf("0 0"); }
    else printf("%d %d\n", ans, ct);
    return 0;
}