'''class Solution {
public:
int lastStoneWeight(vector& stones) {
int n;
while(true){
n = stones.size();
if(n==1||n==0){
break;
}
sort(stones.begin(),stones.end());
int a = stones[n-1];
int b = stones[n-2];
//instead of erase,use pop_back
stones.pop_back();
stones.pop_back();
if(a != b)
stones.push_back(abs(b-a));
}
if(n == 1){
return stones.at(0);
}
else
return 0;
}
};'''