【USACO2017JAN】 Promotion Counting

【题目链接】

            点击打开链接

【算法】

          离散化 + dfs + 树状数组

【代码】

          

#include<bits/stdc++.h>
using namespace std;
#define MAXN 100000

int N,i,lth,x,pos;
int a[MAXN+10],tmp[MAXN+10],rank[MAXN+10],ans[MAXN+10];
vector<int> E[MAXN+10];

template <typename T> inline void read(T &x) {
        int f = 1; x = 0;
        char c = getchar();
        for (; !isdigit(c); c = getchar()) { if (c == '-') f = -f; }
        for (; isdigit(c); c = getchar()) x = (x << 3) + (x << 1) + c - '0';
        x *= f;
}

template <typename T> inline void write(T x) {
    if (x < 0) { putchar('-'); x = -x; }
    if (x > 9) write(x/10);
    putchar(x%10+'0');
}

template <typename T> inline void writeln(T x) {
    write(x);
    puts("");
}

struct BinaryIndexedTree {
        int bit[MAXN+10];
        int lowbit(int x) { return x & -x; }
        inline void modify(int pos) {
                int i;
                for (i = pos; i <= N; i += lowbit(i)) bit[i]++;
        }
        inline int query(int pos) {
                int i,ret = 0;
                for (i = pos; i; i -= lowbit(i)) ret += bit[i];
                return ret;
        }
} BIT;

inline void dfs(int x) {
        int i;
        BIT.modify(rank[x]);
        ans[x] = -BIT.query(rank[x]-1);
        for (i = 0; i < E[x].size(); i++) dfs(E[x][i]);
        ans[x] += BIT.query(rank[x]-1);
}

int main() {
    
        read(N);
        for (i = 1; i <= N; i++) {
                read(a[i]);
                tmp[i] = a[i];
        }
        
        sort(tmp+1,tmp+N+1);
        for (i = 1; i <= N; i++) {
                if (tmp[i] != tmp[i-1]) 
                        tmp[++lth] = tmp[i];
        }
        
        for (i = 1; i <= N; i++) {
                pos = lower_bound(tmp+1,tmp+lth+1,a[i]) - tmp;
                rank[i] = N - pos + 1;
        }
        
        for (i = 2; i <= N; i++) {
                read(x);
                E[x].push_back(i);
        }
        
        dfs(1);
        
        for (i = 1; i <= N; i++) writeln(ans[i]);
        
         return 0;
    
}