题解 | #农场牛类别匹配#

#include <endian.h>
class Solution {
public:
    /**
     * 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可
     *
     * 
     * @param breeds int整型vector 
     * @param target_sum int整型 
     * @return int整型
     */
    int result = 0;
    vector<int> path;
    void backTracking(vector<int>& breeds,int startIndex,int target_sum)
    {
        if (path.size() == 2 && path[0] + path[1] == target_sum)
        {
            result++;
            return;
        }
        for (int i = startIndex;i < breeds.size();++i)
        {
            if (path.size() == 1)
            {
                if (path[0] + breeds[i] > target_sum || breeds[i] >= target_sum)
                {
                    continue;
                }
            }
            path.push_back(breeds[i]);
            backTracking(breeds, i + 1, target_sum);
            path.pop_back();
        }
    }
    int countMatchingPairs(vector<int>& breeds, int target_sum) 
    {
        // write code here
        backTracking(breeds,0,target_sum);
        return result;
    }
};

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