Codeforces 246A-Buggy Sorting【模拟】
2016-05-03 19:28
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A. Buggy Sorting
time limit per test
2 seconds
memory limit per test
256 megabytes
input
standard input
output
standard output
Little boy Valera studies an algorithm of sorting an integer array. After studying the theory, he went on to the practical tasks. As a result, he wrote a program that sorts an array of n integers a1, a2, ..., an in
the non-decreasing order. The pseudocode of the program, written by Valera, is given below. The input of the program gets number n and
array a.
But Valera could have made a mistake, because he hasn't yet fully learned the sorting algorithm. If Valera made a mistake in his program, you need to give a counter-example that makes his program work improperly (that is, the example that makes the program
sort the array not in the non-decreasing order). If such example for the given value of n doesn't exist, print -1.
Input
You've got a single integer n (1 ≤ n ≤ 50) —
the size of the sorted array.
Output
Print n space-separated integers a1, a2, ..., an (1 ≤ ai ≤ 100)
— the counter-example, for which Valera's algorithm won't work correctly. If the counter-example that meets the described conditions is impossible to give, print -1.
If there are several counter-examples, consisting of n numbers, you are allowed to print any of them.
Examples
input
output
time limit per test
2 seconds
memory limit per test
256 megabytes
input
standard input
output
standard output
Little boy Valera studies an algorithm of sorting an integer array. After studying the theory, he went on to the practical tasks. As a result, he wrote a program that sorts an array of n integers a1, a2, ..., an in
the non-decreasing order. The pseudocode of the program, written by Valera, is given below. The input of the program gets number n and
array a.
loop integer variable i from 1 to n - 1 loop integer variable j from i to n - 1 if (aj > aj + 1), then swap the values of elements aj and aj + 1
But Valera could have made a mistake, because he hasn't yet fully learned the sorting algorithm. If Valera made a mistake in his program, you need to give a counter-example that makes his program work improperly (that is, the example that makes the program
sort the array not in the non-decreasing order). If such example for the given value of n doesn't exist, print -1.
Input
You've got a single integer n (1 ≤ n ≤ 50) —
the size of the sorted array.
Output
Print n space-separated integers a1, a2, ..., an (1 ≤ ai ≤ 100)
— the counter-example, for which Valera's algorithm won't work correctly. If the counter-example that meets the described conditions is impossible to give, print -1.
If there are several counter-examples, consisting of n numbers, you are allowed to print any of them.
Examples
input
1
output
-1
解题思路:
上面是一个人写的错误的将一个序列排成递增序列的代码,我们要找到反例,如果找不到就输出-1.
#include<stdio.h> int main() { int n; while(scanf("%d",&n)!=EOF) { if(n<=2) { printf("-1\n"); continue; } for(int i=1;i<n;i++) { printf("%d ",i+1); } printf("1\n"); } return 0; }
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