最长子序列和（分治法实现）
1 #include<iostream> 2 #include<cstring> 3 #include<string> 4 #include<cstdio> 5 #include<vector> 6 #include<cmath> 7 #include<stack> 8 #include<set> 9 #include<queue> 10 #include<algorithm> 11 using namespace std; 12 const long long mod=1000000007; 13 const long long min_=-1000000000; 14 int maxsub(const int a[],int left,int right){ 15 int maxleftsum,maxrightsum; 16 int maxleftbordersum,maxrightbordersum; 17 int leftbordersum,rightbordersum; 18 int center,i; 19 if(left==right) 20 if(a[left]>0) 21 return a[left]; 22 else return 0; 23 center=(left+right)/2; 24 maxleftsum=maxsub(a,left,center); 25 maxrightsum=maxsub(a,center+1,right); 26 maxleftbordersum=leftbordersum=0; 27 for(i=center;i>=left;i--) 28 { 29 leftbordersum+=a[i]; 30 if(leftbordersum>maxleftbordersum) 31 maxleftbordersum=leftbordersum; 32 } 33 maxrightbordersum=rightbordersum=0; 34 for(i=center+1;i<=right;i++) 35 { 36 rightbordersum+=a[i]; 37 if(rightbordersum>maxrightbordersum) 38 maxrightbordersum=rightbordersum; 39 } 40 int t=max(maxleftsum,maxrightsum); 41 return max(t,maxleftbordersum+maxrightbordersum); 42 } 43 int main() 44 { 45 int a[55]; 46 int n; 47 cin>>n; 48 int sum=0; 49 for(int i=0;i<n;i++){ 50 cin>>a[i]; 51 sum+=a[i]; 52 } 53 cout<<maxsub(a,0,n-1)<<" "<<sum<<endl; 54 return 0; 55 }
最长子序列和，产生情况，用分治法就是左边或者右边，或者横跨俩边，
建立base case就是left=right则返回a[left]的值。
分治关键在于后面的和，俩边可以递归实现。
