求最大子数组之和的分治算法

#include <stdio.h>
#include <limits.h>

typedef struct _node
{
    int left;
    int right;
    int sum;
}Node;

void findCrossSubArr(int *arr,int low,int mid,int high,Node *crossResult)
{
      int left_sum=INT_MIN;
      int sum=0;
      int i=mid;
      for(;i>=low;i--)
      {
          sum=sum+arr[i];
          if(sum>left_sum)
          {
              left_sum=sum;
              crossResult->left=i;
          }
      }

      int right_sum=INT_MIN;
      sum=0;
      i=mid+1;
      for(;i<=high;i++)
      {
          sum=sum+arr[i];
          if(sum>right_sum)
          {
              right_sum=sum;
              crossResult->right=i;
          }
      }

      crossResult->sum=left_sum+right_sum;

}

void findMaxSubArr(int *arr,int low,int high,Node *result)
{
     if(low==high)
     {
         result->left=low;
         result->right=low;
         result->sum=arr[low];
         return;
     }

     int mid=(low+high)>>1;
     Node leftResult;
     Node rightResult;

     findMaxSubArr(arr,low,mid,&leftResult);
     findMaxSubArr(arr,mid+1,high,&rightResult);

     Node crossResult;
     findCrossSubArr(arr,low,mid,high,&crossResult);

     if((leftResult.sum)>=(rightResult.sum)&&(leftResult.sum)>=(crossResult.sum))
     {
         result->left=leftResult.left;
         result->right=leftResult.right;
         result->sum=leftResult.sum;
         return ;
     }

     else if((rightResult.sum)>=(leftResult.sum)&&(rightResult.sum)>=(crossResult.sum))
     {
         result->left=rightResult.left;
         result->right=rightResult.right;
         result->sum=rightResult.sum;
         return ;
     }

     else
     {
         result->left=crossResult.left;
         result->right=crossResult.right;
         result->sum=crossResult.sum;
         return ;
     }

}

int main()
{
    Node result;
    int arr[]={1,-2,3,10,-4,7,2,-5};
    int len=sizeof(arr)/sizeof(arr[0]);
    findMaxSubArr(arr,0,len-1,&result);
    printf("%d\n",result.left);
    printf("%d\n",result.right);
    printf("%d\n",result.sum);
    system("pause");
    return 0;
}

来源：https://www.cnblogs.com/liguigen/p/liguigen_blog.html

标签

分治算法

return