Codeforces Round #191 (Div. 2)---A. Flipping Game
2014-12-29 20:47
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Flipping Game
time limit per test
1 second
memory limit per test
256 megabytes
input
standard input
output
standard output
Iahub got bored, so he invented a game to be played on paper.
He writes n integers a1, a2, ..., an.
Each of those integers can be either 0 or 1. He's allowed to do exactly one move: he chooses two indices i and j (1 ≤ i ≤ j ≤ n)
and flips all values ak for
which their positions are in range [i, j] (that is i ≤ k ≤ j).
Flip the value of xmeans to apply operation x = 1 - x.
The goal of the game is that after exactly one move to obtain the maximum number of ones. Write a program to solve the little game of Iahub.
Input
The first line of the input contains an integer n (1 ≤ n ≤ 100).
In the second line of the input there are n integers: a1, a2, ..., an.
It is guaranteed that each of those n values is either 0 or 1.
Output
Print an integer — the maximal number of 1s that can be obtained after exactly one move.
Sample test(s)
input
output
input
output
Note
In the first case, flip the segment from 2 to 5 (i = 2, j = 5). That flip changes the sequence, it becomes: [1 1 1 0 1]. So, it contains four ones.
There is no way to make the whole sequence equal to [1 1 1 1 1].
In the second case, flipping only the second and the third element (i = 2, j = 3) will turn all numbers into 1.
解题思路:题意是讲有一个0,1序列,现同意你对随意一个子序列取反,问操作后得到的序列,最多能有多少个1。
数据不大,直接暴力。直接两层循环枚举取反序列的起点和终点,统计每种情况下1的个数,保存一个最大值就可以。
AC代码:
time limit per test
1 second
memory limit per test
256 megabytes
input
standard input
output
standard output
Iahub got bored, so he invented a game to be played on paper.
He writes n integers a1, a2, ..., an.
Each of those integers can be either 0 or 1. He's allowed to do exactly one move: he chooses two indices i and j (1 ≤ i ≤ j ≤ n)
and flips all values ak for
which their positions are in range [i, j] (that is i ≤ k ≤ j).
Flip the value of xmeans to apply operation x = 1 - x.
The goal of the game is that after exactly one move to obtain the maximum number of ones. Write a program to solve the little game of Iahub.
Input
The first line of the input contains an integer n (1 ≤ n ≤ 100).
In the second line of the input there are n integers: a1, a2, ..., an.
It is guaranteed that each of those n values is either 0 or 1.
Output
Print an integer — the maximal number of 1s that can be obtained after exactly one move.
Sample test(s)
input
5 1 0 0 1 0
output
4
input
41 0 0 1
output
4
Note
In the first case, flip the segment from 2 to 5 (i = 2, j = 5). That flip changes the sequence, it becomes: [1 1 1 0 1]. So, it contains four ones.
There is no way to make the whole sequence equal to [1 1 1 1 1].
In the second case, flipping only the second and the third element (i = 2, j = 3) will turn all numbers into 1.
解题思路:题意是讲有一个0,1序列,现同意你对随意一个子序列取反,问操作后得到的序列,最多能有多少个1。
数据不大,直接暴力。直接两层循环枚举取反序列的起点和终点,统计每种情况下1的个数,保存一个最大值就可以。
AC代码:
#include <iostream> #include <cstdio> using namespace std; int a[105]; int main(){ // freopen("in.txt","r",stdin); int n; while(cin>>n){ for(int i =0; i<n; i++) cin>>a[i]; int ans = 0; for(int i=0; i<n; i++){ for(int j=i; j<n; j++){ int sum = 0; for(int k=0; k<n; k++){ if(k>=i && k<=j) sum += a[k]^1; //用异或^取反 else sum += a[k]; } if(ans < sum) ans = sum; } } cout<<ans<<endl; } return 0; }
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