分治——最大数组和

 1 #include<iostream>
 2 using namespace std; 
 3 struct sub{      //定义一个子数组起点，终点与其所有元素和
 4     int start;
 5     int end;
 6     
 7     int sum;
 8 };
 9 
10 sub merge(sub sub1,int start,int end,int A[]) //
11 {
12     int leftSum=0,rightSum=0,leftPos=(start+end)/2,rightPos=(start+end)/2+1,leftMax=-10000,rightMax=-10000;
13 
14     for(int i=(start+end)/2;i>=start;i--)
15     {
16         leftSum+=A[i];    //求最大数组和的起点
17         if(leftMax<leftSum)
18         {
19             leftPos=i;
20             leftMax=leftSum;            
21         }
22     }
23     
24     for(int i=(start+end)/2;i<=end;i++)
25     {
26          rightSum+=A[i];
27         if(rightMax<rightSum)   //求最大数组和的终点
28         {
29             rightPos=i;
30             rightMax=rightSum;            
31         }
32     }
33     
34     if ( sub1.sum< (rightMax+leftMax) )
35     {
36          sub1.start=leftPos;
37         sub1.end=rightPos;
38         sub1.sum= (rightMax+leftMax);
39     }    
40     
41     return sub1;
42 }
43 sub recursion(int start,int end,int A[])
44 {
45     sub sub1,sub2;
46     
47     if(start<end)
48     {
49         sub1=recursion(start,(start+end)/2,A);
50         sub2=recursion((start+end)/2+1,end,A);    
51         
52         sub1=sub1.sum>sub2.sum?sub1:sub2;
53         
54         return merge(sub1,start,end,A);
55     }
56     
57     sub1.start=sub1.end=start;
58     sub1.sum=A[start];
59     
60     return sub1; 
61 }
62 int main()
63 {
64     int a[]={1,-5,9,8,-3,-6,11};
65     
66     sub sub1=recursion(0,6,a);
67     
68     cout<<sub1.start<<" to "<<sub1.end<<" sum:"<<sub1.sum<<endl; 
69     
70 }
71