Codeforces 551C - GukiZ hates Boxes (二分 + 貪心)

題意

有n堆東西，m個人，每個人在每一秒只能選擇走到下一堆或者拿掉一個東西，問拿掉全部東西最少要多久。

思路

二分時間。

Check的時候，我們可以先拿出一個人，走到最近的非零堆，然後儘可能地搬東西，重複m次，看能不能搬完。

代碼裏的Check寫得有點醜（ ＴДＴ）

代碼

#include <stack>
#include <cstdio>
#include <list>
#include <cassert>
#include <set>
#include <fstream>
#include <iostream>
#include <string>
#include <sstream>
#include <vector>
#include <queue>
#include <functional>
#include <cstring>
#include <algorithm>
#include <cctype>
//#pragma comment(linker, "/STACK:102400000,102400000")
#include <string>
#include <map>
#include <cmath>
//#include <ext/pb_ds/assoc_container.hpp>
//#include <ext/pb_ds/hash_policy.hpp>
using namespace std;
//using namespace __gnu_pbds;
#define LL long long
#define ULL unsigned long long
#define SZ(x) (int)x.size()
#define Lowbit(x) ((x) & (-x))
#define MP(a, b) make_pair(a, b)
#define MS(arr, num) memset(arr, num, sizeof(arr))
#define PB push_back
#define X first
#define Y second
#define ROP freopen("input.txt", "r", stdin);
#define MID(a, b) (a + ((b - a) >> 1))
#define LC rt << 1, l, mid
#define RC rt << 1|1, mid + 1, r
#define LRT rt << 1
#define RRT rt << 1|1
#define FOR(i, a, b) for (int i=(a); (i) < (b); (i)++)
#define FOOR(i, a, b) for (int i = (a); (i)<=(b); (i)++)
const double PI = acos(-1.0);
const int INF = 0x3f3f3f3f;
const double eps = 1e-4;
const int MAXN = 1e5+10;
const int MOD = 8e4+7;
const int dir[][2] = { {-1, 0}, {1, 0}, {0, -1}, {0, 1} };
const int seed = 131;
int cases = 0;
typedef pair<int, int> pii;

int tmp[MAXN], arr[MAXN], n, pos, m;
void Solve(LL mid)
{
    bool first = true;
    LL rem = mid;
    while (true)
    {
        if (pos == n) return;
        while (!tmp[pos])
        {
            pos++;
            if (!first) rem--;
            if (pos == n) return;
        }
        if (first) rem -= (pos+1);
        first = false;
        if (rem <= 0) return;
        if (tmp[pos] > rem)
        {
            tmp[pos] -= rem;
            break;
        }
        else
        {
            rem -= tmp[pos];
            pos++;
            rem--;
        }
    }
}

bool Check(LL mid)
{
    pos = 0;
    copy(arr, arr+n, tmp);
    for (int i = 0; i < m; i++)
        Solve(mid);
    return pos == n;
}

int main()
{
    //ROP;
    scanf("%d%d", &n, &m);
    for (int i = 0; i < n; i++) scanf("%d", &arr[i]);
    LL l = 0, r = (1ll<<60);
    while (l < r)
    {
        LL mid = MID(l, r);
        if (Check(mid)) r = mid;
        else l = mid+1;
    }
    printf("%I64d\n", r);
    return 0;
}