merge_example_spoj_brckts.cpp

#include"segment_tree.cpp"
#include"algorithm"
#include"stdio.h"
struct node{
  int min,sum;
	void merge(node& l,node& r){
		sum = l.sum+r.sum;
		min = std::min(l.min,l.sum+r.min);
	}
};
void flip(node& n){
	n.min*=-1;
	n.sum=n.min;
}
int main(){
	for(int i=0;i<10;i++){
		printf("Test %d:\n",i+1);
		segtree<node> s;
		int n;
		scanf("%d",&n);
		char inp[n+1];
		scanf("%s",inp);
		node arr[n+1];
		for(int i=0;i<n;i++)
			arr[i].min=arr[i].sum=inp[i]=='('?1:-1;
		arr[n].min=arr[n].sum=0;
		s.init(n,arr,arr[n]);
		int m;
		scanf("%d",&m);
		while(m--){
			int k;
			scanf("%d",&k);
			if(k)
				s.update<&flip>(k-1);
			else{
				node x=s.query(0,100000000);
				printf("%s\n",(x.sum==0&&x.min==0)?"YES":"NO");
			}
		}
	}
}

can you explain a little bit that how your code is able to solve the problem