leetcode 679

class Solution {
public:
    const double eps = 1e-6;
    bool judgePoint24(vector<int>& nums) {
        vector<double>l;
        for(int i=0;i<nums.size();i++){
            l.push_back(nums[i]);
        }
        return solve(l);
    }
    bool solve(vector<double> &l){
        if(l.size() == 0)
            return false;
        if(l.size() == 1){
            return (fabs(l[0] - 24) <= eps);
        }
        int size = l.size();
        for(int i=0;i<size;i++){//第i个和第j个元素运算
            for(int j=0;j<size;j++){
                if(i == j)
                    continue;
                vector<double>temp;
                for(int k=0;k<size;k++){
                    if(k!=i&&k!=j)
                        temp.push_back(l[k]);//其他元素不影响
                }
                //+,-,*,/
                for(int k=1;k<=4;k++){
                    if(k == 1){
                        temp.push_back(l[i] + l[j]);
                    }
                    if(k == 2){
                        temp.push_back(l[i] - l[j]);
                    }
                    if(k == 3){
                        temp.push_back(l[i] * l[j]);
                    }
                    if(k == 4){
                        if(fabs(l[j]) <= eps){
                            continue;
                        }
                        temp.push_back(l[i]/l[j]);
                    }         
                if(solve(temp))
                    return true;
                temp.pop_back();
                }
       
            }
        }
        return false;
    }
};