Sicily 周赛 Opening Ceremony

Description

For the grand opening of the algorithmic games in NlogNsglow, a row of tower blocks is set to be demolished in a grand demonstration of renewal. Originally the plan was to accomplish this with controlled explosions, one for each tower block, but time constraints now require a hastier solution.

To help you remove the blocks more rapidly you have been given the use of a Universal Kinetic / Incandescent Energy Particle Cannon (UKIEPC). On a single charge, this cutting-edge contraption can remove either all of the floors in a single tower block, or all the x-th floors in all the blocks simultaneously, for user’s choice of the floor number x. In the latter case, the blocks that are less than x floors high are left untouched, while for blocks having more than x floors, all the floors above the removed x-th one fall down by one level.

Given the number of floors of all towers, output the minimum number of charges needed to eliminate all floors of all blocks.

Input

The first line of input contains the number of blocks n, where 2 <= n <= 100 000. The second line contains n consecutive block heights hi for i = 1, 2, ..., n, where 1 <= hi <= 1 000 000.

Output

Output one line containing one integer: the minimum number of charges needed to tear down all the blocks.

Sample Input

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样例一：62 1 8 8 2 3样例二：51 1 1 1 10

Sample Output

样例一：5样例二：2

题解：

排序之后看非零楼的数目，还有最高楼的数目，两者消去最大值。

类似贪心算法。

比如这样，看红色区域还有黄色区域谁大消谁。

代码：

#include <cstdio>#include <algorithm>using namespace std;int arr[100005];int main(){int n ;while(~scanf("%d",&n)){long long sum = 0 ,cur = 0;for(int i = 0;i < n;i++){scanf("%d",&arr[i]);sum += arr[i];}sort(arr, arr + n);int l = 0 ,r = n - 1;int cnt = 0;int height = 1 ;while(cur < sum){if((r - l + 1) <= (arr[r] - height + 1)){cur += (arr[r] - height + 1);r--;}else{cur += (r - l + 1);   //用个height记录，循环每层减一会超时 while(arr[l]<=height)l++;height++;}cnt++;}printf("%d\n",cnt);}}