[Codeforces 466C] Number of Ways

[题目链接]

https://codeforces.com/contest/466/problem/C

[算法]

维护序列前缀和 ， 枚举中间一段即可 ， 详见代码

时间复杂度 ： O(N)

[代码]

#include<bits/stdc++.h>
using namespace std;
const int MAXN = 5e5 + ;

int a[MAXN];
long long sum[MAXN];

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

int main()
{

        int n;
        read(n);
        for (int i = ; i <= n; i++)
        {
                read(a[i]);
                sum[i] = sum[i - ] + a[i];
        }
        if (sum[n] %  != )
        {
                printf("0\n");
                return ;
        }
        long long value = sum[n] /  , ans =  , cnt = ;
        for (int i = ; i < n; i++)
        {
                if (sum[i] !=  * value)
                {
                        if (sum[i] == value) cnt++;
                        continue;
                }
                ans += cnt;
                if (sum[i] == value) cnt++;
        }
        printf("%I64d\n",ans);

        return ;

}