Codeforces Round #262(div2) C. Present

http://codeforces.com/contest/460/problem/C

C. Present

time limit per test

2 seconds

memory limit per test

256 megabytes

input

standard input

output

standard output

Little beaver is a beginner programmer, so informatics is his favorite subject. Soon his informatics teacher is going to have a birthday and the beaver has decided to prepare a present for her. He planted n flowers in a row on his windowsill and started waiting for them to grow. However, after some time the beaver noticed that the flowers stopped growing. The beaver thinks it is bad manners to present little flowers. So he decided to come up with some solutions.

There are m days left to the birthday. The height of the i-th flower (assume that the flowers in the row are numbered from 1 to n from left to right) is equal to ai at the moment. At each of the remaining m days the beaver can take a special watering and water w contiguous flowers (he can do that only once at a day). At that each watered flower grows by one height unit on that day. The beaver wants the height of the smallest flower be as large as possible in the end. What maximum height of the smallest flower can he get?

Input

The first line contains space-separated integers n, m and w (1 ≤ w ≤ n ≤ 105; 1 ≤ m ≤ 105). The second line contains space-separated integers a1, a2, ..., an (1 ≤ ai ≤ 109).

Output

Print a single integer — the maximum final height of the smallest flower.

Sample test(s)

input

6 2 3
2 2 2 2 1 1

output

2

input

2 5 1
5 8

output

9

Note

In the first sample beaver can water the last 3 flowers at the first day. On the next day he may not to water flowers at all. In the end he will get the following heights: [2, 2, 2, 3, 2, 2]. The smallest flower has height equal to 2. It's impossible to get height 3 in this test.

题解：

         二分查找，状态是否满足的判断，从前往后判断差值，与要判断的差值是多少，往后的这段w长度区间都增加多少，天数加1，判断最后会不会超过总天数。

代码：

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
#define mem(a, b) memset (a, b, sizeof (a) )
#define reply(i, a, b, c) for (long long i = a; i <= b; i += c)
using namespace std;
const long long maxn = 500000+ 111;
const long long ef = (long long)1<<45;
long long n, m, w, minn;
long long a[maxn], b[maxn];
int solve (long long k) {

    mem (b, 0);

    long long temp = 0, cost = 0;

    reply (i, 1, n, 1) {

        temp += b[i];

        long long tmp = k - (a[i] + temp);

        if (tmp > 0) {

            b[i+1] += tmp;

            b[i+w] -= tmp;

            cost += tmp;

        }

    }

    return cost <= m;

}

void solve () {

    long long l = 0, r = ef , ans = minn;

    while (l <= r) {

        long long m = (l + r) >> 1;

        if (solve(m))
        {
            ans = max(ans, m);
            l = m + 1;
        }
        else r = m -1;
    }
    cout<<ans<<endl;

}

int main() {

    while (~scanf("%I64d%I64d%I64d",&n,&m,&w))
    {
        minn = ef;
        reply (i, 1, n, 1) {
            scanf ("%I64d", & a[i]);
            minn = min (minn, a[i]);

        }
        solve();
    }

    return 0;
}