【POJ-1456】 Supermarket

#include <iostream>
#include <algorithm>
#include <vector>
using namespace std;

const int SIZE = 1 << 20;
vector<pair <int,int> > vec;
int fa[SIZE];

bool cmp(pair<int,int> a,pair<int,int> b) {
	return a.first > b.first;
}

int get(int x) {
	if (x == fa[x]) return x;
	return fa[x] = get(fa[x]);
}

void merge(int x,int y) {
	fa[get(x)] = get(y);
}

int main() {
	int n;
	while (cin >> n) {
		int ans = 0, maxn = 0; vec.clear();
		int a, b;
		for (int i = 1; i <= n; ++i) {
			cin >> a >> b;
			vec.push_back(make_pair(a,b));
			maxn = max(maxn, b);
		}
		sort(vec.begin(), vec.end(), cmp);
		for (int i = 0; i <= maxn ; ++i) {
			fa[i] = i;
		}
		for (int i = 0; i < n; ++i) {
			int w = vec[i].first, v = vec[i].second;
			int root = get(v);
			if (root > 0) {
				ans += w; merge(root,root-1);
			}
		}
		cout << ans << endl;
	}
	return 0;
}