【USACO】 Balanced Photo

【题目链接】

点击打开链接

【算法】

树状数组

【代码】

#include<bits/stdc++.h>

using namespace std;

int i,N,ans,l1,l2;
int c[],val[],id[];

template <typename T> void read(T &x) {
        int f=; char c = getchar(); x=;
        for (; !isdigit(c); c = getchar()) { if (c=='-') f=-; }
        for (; isdigit(c); c = getchar()) x=x*+c-'';
        x*=f;
}

bool cmp(int a,int b) {
        return val[a] > val[b];
}

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

int query(int x) {
        int sum=;
        while (x >= ) {
              sum += c[x];
              x -= lowbit(x);
        }
        return sum;
}

void change(int x,int y) {
        while (x <= N) {
                c[x] += y;
                x += lowbit(x);
        }
}

int main() {

        scanf("%d",&N);
        for (i = ; i <= N; i++) {
                scanf("%d",&val[i]);
                id[i] = i;
        }
        sort(id+,id+N+,cmp);

        for (i = ; i <= N; i++) {
                l1 = query(id[i]-);
                l2 = i - l1 - ;
                if (max(l1,l2) > min(l1,l2) * ) ans++;
                change(id[i],);
        }

        printf("%d\n",ans);

        return ;

}