剑指Offer34 数组中的逆序对

 /*************************************************************************
     > File Name: 34_InversePairsInArray.c
     > Author: Juntaran
     > Mail: JuntaranMail@gmail.com
     > Created Time: 2016年09月02日 星期五 20时05分05秒
  ************************************************************************/

 #include <stdio.h>
 #include <malloc.h>

 int InversePairsCore(int* nums, int* copy, int left, int right)
 {
     if (left == right)
     {
         copy[left] = copy[right];
         return ;
     }
     int newlength = (right - left) / ;

     // 递归
     int leftCount  = InversePairsCore(copy, nums, left, left+newlength);
     int rightCount = InversePairsCore(copy, nums, left+newlength+, right);

     // i初始化为前半段最后一个数字下标
     int i = left + newlength;
     // j初始化为后半段最后一个数字下标
     int j = right;

     int indexCopy = right;
     int count = ;

     while (i>=left && j>=left+newlength+)
     {
         if (nums[i] > nums[j])
         {
             copy[indexCopy--] = nums[i--];
             count += j - left - newlength;
         }
         else
         {
             copy[indexCopy--] = nums[j--];
         }
     }

     for (i; i >= left; --i)
         copy[indexCopy--] = nums[i];
     for (j; j>=left+newlength+; --j)
         copy[indexCopy--] = nums[j];

     return leftCount + rightCount + count;
 }

 int InversePairs(int* nums, int length)
 {
     if (nums==NULL || length<=)
         return -;

     int* copy = (int*)malloc(sizeof(int)*length);
     for (int i = ; i < length; ++i)
         copy[i] = nums[i];

     int count = InversePairsCore(nums, copy, , length-);
     delete[] copy;

     return count;
 }

 int main()
 {
     int nums[] = {,,,};
     int length = ;
     int ret = InversePairs(nums, length);
     printf("%d\n", ret);
 }