Codeforces Round #261 (Div. 2) D 樹狀數組應用

Codeforces Round #261 (Div. 2) D 樹狀數組應用

看著題意：[1,i]中等於a[i]的個數要大於[,jn]中等於a[j]的個數 且i

int n;

int aa[1000000 + 55];
int bb[1000000 + 55];

int c[1000000 + 55];

map	mp;

ll lowbit(ll x) {
	return x&(-x);
}

void add(int i,int val) {
	while(i <= n) {
		c[i] += val;
		i += lowbit(i);
	}
}

ll get_sum(int i) {
	ll sum = 0;
	while(i) {
		sum += c[i];
		i -= lowbit(i);
	}
	return sum;
}

void init() {
	memset(c,0,sizeof(c));
	memset(aa,0,sizeof(aa));
	memset(bb,0,sizeof(bb));
	mp.clear();
}

int main() {
	while(scanf("%d",&n) == 1) {
		init();
		for(int i=1;i<=n;i++)scanf("%d",&aa[i]);
		for(int i=1;i<=n;i++) {
			mp[aa[i]]++;
			bb[i] = mp[aa[i]];
			add(bb[i],1);
		}
		mp.clear();
		ll ans = 0ll;
		for(int i=n;i>=1;i--) {
			add(bb[i],-1);
			mp[aa[i]]++;
			int tmp = mp[aa[i]];
			ans += i - get_sum(tmp) - 1;
		}
		cout<