B题贪心

class Solution {
public:
 long long wwork(int n, int m, vector<int>& a, vector<vector<int> >& b) {
     long long ans=0;
     vector<long long> aa(n);
     for (int i=0;i<n;i++) {
         aa.at(i)=a.at(i);
     }
     for (vector<int> &i:b) {
         int x=i.at(0)-1;
         int y=i.at(1)-1;
         int z=i.at(2);
         aa.at(x)+=z;
         aa.at(y)+=z;
         ans-=z;
     }
     for (int i=0;i<n;++i) {
         ans+=max(aa.at(i),0LL);
     }
     return ans;
 }
};