ACM-ICPC 2018 徐州赛区网络预赛 H题

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题目链接：Ryuji doesn’t want to study

思路

区间询问，单点修改，用树状数组，维护区间和信息。

AC代码

#include<cstdio>
#include<vector>
using namespace std;

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

struct FenwickTree {
  int n;
  vector<long long> C;

  void resize(int n) { this->n = n; C.resize(n); }
  void clear() { fill(C.begin(), C.end(), 0); }

  // 计算A[1]+A[2]+...+A[x] (x<=n)
  long long sum(int x) {
    long long ret = 0;
    while(x > 0) {
      ret += C[x]; x -= lowbit(x);
    }
    return ret;
  }

  // A[x] += d (1<=x<=n)
  void add(int x, long long d) {
    while(x <= n) {
      C[x] += d; x += lowbit(x);
    }
  }

  long long get(int l, int r) {
    return sum(r)-sum(l-1);
  }
};

const int maxn = 200000 + 5;
int a[maxn];
FenwickTree f, p;


int main() {
    int n, q;
    while(scanf("%d%d", &n, &q) == 2) {
        for(int i = 1; i <= n; i++) {
            scanf("%d", &a[i]);
        }
        f.resize(n);
        f.clear();
        p.resize(n);
        p.clear();
        for(int i = 1; i <= n; i++) {
            f.add(i, a[i]);
            p.add(i, 1LL*a[i]*i);
        }   
        int cmd;
        for(int i = 0; i < q; i++) {
            int x, y;
            scanf("%d%d%d", &cmd, &x, &y);
            if(cmd == 1) {
                long long ans = 1LL * (y+1) * f.get(x, y) - 1LL * p.get(x, y);
                //long long ans = f.get(x, y);
                printf("%lld\n", ans);
            } else {
                f.add(x, y - a[x]);
                p.add(x, 1LL*y*x - 1LL*a[x]*x);
                a[x] = y;
            }
        }
    }
    return 0;
}

如有不当之处欢迎指出！