Luo Gu P1496 Huoshaochibi (discrete entry)

Discretization

The aim is to map discrete individual large section to a smaller interval, enhance space efficiency, used to find the relative position of the current position of the source sequence number in

    for(int i=1;i<=n;++i){
        t[i] = a[i];
    }
    sort(t+1,t+1+n);
    end = unique(t+1,t+1+n)-t-1;    // unique 返回去重后数组尾地址, end 为数组尾下标
    for(int i=1;i<=n;++i){
        a[i] = lower_bond(t+1,t+m+1,a[i])-t;// 在t中二分查找a[i] 再减去首地址 即可得到相对大小
    }

Topic: luogo P1496 Huoshaochibi

• Title effect: Gives \ (n-\) line segments, the length required to cover
• Ideas: first of all the left and right endpoints discrete, ordered into several sections, with a differential array record a valid location, the difference array is updated prefix and the interval greater than zero

#include<bits/stdc++.h>
#define ll long long 
#define FOR(i,n) for(int i =1; i <= n;++i ) 
#define FOR0(i,n) for(int i =0; i < n;++i )  
#define inf 0x3f3f3f3f
#define EPS (1e-8)
#define ALL(T)  T.begin(),T.end()
using namespace std;

const int maxn = 5e5+40;
int n;
int t[maxn],a[maxn],b[maxn],add[maxn];
int main(){
    cin >> n;
    FOR(i,n){
        cin >> a[i] >> b[i];
        t[i*2-1] = a[i];
        t[i*2] = b[i];
    }
    sort(t+1,t+1+n+n);

    int m = unique(t+1,t+1+n+n)-t-1;
    for(int i=1;i<=n;++i){
        a[i] = lower_bound(t+1,t+m+1,a[i])-t;
        b[i] = lower_bound(t+1,t+1+m,b[i])-t;
        add[a[i]]++;        //原从 a[i] 到 b[i] 加 1
        add[b[i]]--;
    }
    int temp=0,ans=0;
    FOR(i,m){
        temp+=add[i];
        // cout << add[i] << ' '<< t[i] << endl;
        if(temp > 0){
            // 当前区间可用,更新右端点
            ans = ans + t[i+1] - t[i];
        }
    }
    cout << ans << endl;
    return 0;
}

Feeling with the prefix and is very clever.
Title
discrete blog