用分治法求最大子段和
这是我的代码,但是一运行就出现如下结果:
#include <iostream>
using namespace std;
//使用分治算法
int maxSubSum(int* a,int left,int right,int &start,int &end)
{
int sum=0;
if(left==right)
{
sum=a[left]>0? a[left]:0;
start=end=left;
}
else
{
int center=(left+right)/2;
int leftSum=maxSubSum(a,left,center,start,end);
int rightSum=maxSubSum(a,center+1,right,start,end);
int s1=0;
int lefts=0;
for(int i=center;i>=left;i--)
{
lefts+=a[i];
if(lefts>s1)
{
s1=lefts;
start=i;
}
}
int s2=0;
int rights=0;
for(int i=center;i<=right;i--)
{
lefts+=a[i];
if(rights>s2)
{
s2=rights;
end=i;
}
}
sum=s1+s2;
if(sum<leftSum)
sum=leftSum;
if(sum<rightSum)
sum=rightSum;
}
return sum;
}
int maxSum(int *a,int n,int &start,int &end)
{
return maxSubSum(a,0,n,start,end);
}
int main()
{
int number;
cin>>number;
for(int j=1;j<=number;j++)
{
int n,start,end,maxsum;
cin>>n;
int *a=new int[n];
for(int i=0;i<n;i++)
{
cin>>a[i];
}
// for(int i=0;i<n;i++)
// {
// int thisSum=0;
// for(int k=i;k<n;k++)
// {
// thisSum+=a[k];
// if(thisSum>maxSum)
// {
// maxSum=thisSum;
// start=i;
// end=k;
// }
// }
// }
maxsum=maxSum(a,n-1,start,end);
cout<<"Case "<<j<<":"<<endl;
cout<<maxsum<<" "<<++start<<" "<<++end;
if(j!=number)
cout<<endl<<endl;
else
cout<<endl;
}
return 0;
}
int s2=0;
int rights=0;
for(int i=center;i<=right;i--)
{
lefts+=a[i]; // 不懂代码什么原理,不过这里的lefts是不是写错了,应该用rights吧???
if(rights>s2)
{
s2=rights;
end=i;
}
}
题意：最大子段和
思路：见博客的链接
注意：犯很低级的错误，找一个数组的最大值的时候wa啦一次！
#include <iostream>
#include<cstring>
#define MAX 10010
int a[MAX],dp[MAX];
using namespace std;
int main()
{
int n,i,m;
while(cin >> n&&n)
{
memset(dp,0,sizeof(dp));
m=0;
for(i=1; i<=n; i++)
cin >> a[i];
for(i=1; i<=n; i++)
{
dp[i+1]=a[i]+max(dp[i],0);
if(dp[i+1]>m) m=dp[i+1];
}
if(m>0) cout << "The maximum winning streak is " << m << "." << endl;
else cout << "Losing streak." << endl;
}
return 0;
}
//分治法
#include <iostream>
using namespace std;
int maxsum(int a[],int left,int right)
{
int sum=0;
int i,j,s1,s2,lefts,rights,center,leftsum,rightsum;
if(left==right)
{
if(a[left]>0)
sum=a[left];
else
sum=0;
}
else
{
center=(left+right)/2;
leftsum=maxsum(a,left,center);
rightsum=maxsum(a,center+1,right);
s1=0;lefts=0;
for(i=center;i>=left;i--)
{
lefts+=a[i];
if(lefts>s1)
s1=lefts;
}
s2=0;rights=0;
for(j=center+1;j<=right;j++)
{
rights+=a[j];
if(rights>s2)
s2=rights;
}
sum=s1+s2;
if(sum<leftsum)
sum=leftsum;
if(sum<rightsum)
sum=rightsum;
}
return sum;
}
void main()
{
int a[100];
int n,i,l,r;
cout<<"输入序列元素个数:";
cin>>n;
cout<<"输入序列元素:"<<endl;
for(i=1;i<=n;i++)
cin>>a[i];
l=n%2;
r=n-l;
cout<<"最大子段和为:"<<maxsum(a,l,r)<<endl;
}
