牛客排列计算(思维)

思路:出现次数越多我们让他的值越大，用差分统计出现次数，排序后乘以位置就是贡献

#include <cstdio>
#include <cstring>
#include <algorithm>
#include <set>
#include<bits/stdc++.h>
using namespace std;
typedef long long ll;
#define space putchar(' ')
#define enter putchar('\n')
typedef pair<int ,int> PII;
const int mod=1e9+7;
const int N=3e6+7;
int a[N],s[N];

  ll gcd(ll a,ll b){ return b==0?a:gcd(b,a%b); }

ll lcm(ll a,ll b)
{
    return a*(b/gcd(a,b));
}

template <class T>
void read(T &x){
    char c;
    bool op = 0;
    while(c = getchar(), c < '0' || c > '9')
	if(c == '-') op = 1;
    x = c - '0';
    while(c = getchar(), c >= '0' && c <= '9')
	x = x * 10 + c - '0';
    if(op) x = -x;
}
template <class T>
void write(T x){
    if(x < 0) x = -x, putchar('-');
    if(x >= 10) write(x / 10);
    putchar('0' + x % 10);
}

int main()
{
    int n,m;
    read(n),read(m);
    for(int i=1;i<=m;i++)
    {
        int l,r;
        read(l),read(r);
        a[l]++,a[r+1]--;
    }
    for(int i=1;i<=n;i++)
    {
        a[i]+=a[i-1];

    }
    sort(a+1,a+1+n);
    
    ll ans=0;
    for(int i=1;i<=n;i++)
        ans+=1ll*a[i]*i;
    write(ans);



    return 0;
}