leetcode-剑指51-OK

// language C with STL(C++)
// 剑指51
// https://leetcode-cn.com/problems/shu-zu-zhong-de-ni-xu-dui-lcof/


class Solution {
public:
	int core(vector<int>& nums,int low,int high){
		if(high-low <=0)
			return 0;
		int mid = (low + high)/2;
		int res = core(nums, low,mid) +core(nums, mid+1, high);
		int i = low, j = mid +1-low, k = low;
		int fuzhu[high-low+1];	// 0号对应着low号
		for(;i<=high; i++){
			fuzhu[i-low] = nums[i];
		}
		for(i=0; i<mid+1-low && j<=high-low;k++){
			if(fuzhu[i]<=fuzhu[j]){
				nums[k] = fuzhu[i];
				i++;
			}else{
				nums[k] = fuzhu[j];
				j++;
				res += mid+1-low-i;
			}
		}
		while(i<mid+1-low){
			nums[k++] = fuzhu[i++];
		}
		while(j<=high-low){
			nums[k++] = fuzhu[j++];
		}
		return res;
	}
    int reversePairs(vector<int>& nums) {
    	return core(nums,0, nums.size()-1);
    }
};