标签：codeforces
题目链接：http://codeforces.com/contest/454/problem/B
One day, Twilight Sparkle is interested in how to sort a sequence of integers a1,?a2,?...,?an in non-decreasing order. Being a young unicorn, the only operation she can perform is a unit shift. That is, she can move the last element of the sequence to its beginning:
Help Twilight Sparkle to calculate: what is the minimum number of operations that she needs to sort the sequence?
The first line contains an integer n (2?≤?n?≤?105). The second line contains n integer numbers a1,?a2,?...,?an (1?≤?ai?≤?105).
If it‘s impossible to sort the sequence output -1. Otherwise output the minimum number of operations Twilight Sparkle needs to sort it.
2 2 1
1
3 1 3 2
-1
2 1 2
0
思路：
判断有存在几个“下坡”，也就是后面的数比前面的小；
如果没有则输出0；如果有不止一个，则输出-1；如果恰有一个， 那么就需要判断a[1]和a[n]的大小关系；
代码如下：
#include <cstdio>
#include <cstring>
int main()
{
int n;
int i, j;
int a[100017];
while(~scanf("%d",&n))
{
for(i = 1; i <= n; i++)
{
scanf("%d",&a[i]);
}
int cont = 0;
int t;
for(i = 2; i <= n; i++)
{
if(a[i] < a[i-1])
{
cont++;
t = i;
}
}
if(cont == 0)
printf("0\n");
else if(cont > 1)
printf("-1\n");
else if(cont == 1 && a[n] <= a[1])
printf("%d\n",n-t+1);
else
printf("-1\n");
}
return 0;
}
Codeforces Round #259 (Div. 2) （序列）,布布扣,bubuko.com
Codeforces Round #259 (Div. 2) （序列）
标签：codeforces
原文地址：http://blog.csdn.net/u012860063/article/details/38350805
