【P1496】 火烧赤壁 离散化 +差分

code

#include <iostream>
#include <cctype>
#include <cstdio>
#include <algorithm>
#include <vector>
#include <cstring>

using namespace std;
inline int read(){
    
    
    int x = 0, op = 1; char ch = getchar();
    while (!isdigit(ch)){
    
    
        if (ch == '-') op = -1; ch = getchar();}
    while (isdigit(ch)){
    
    
        x = (x << 1) + (x << 3) + (ch ^ 48);
        ch = getchar();
    }
    return x * op;
}
const int N = 2e4 + 10;
int a[N], b[N], diff[N];
vector<int> v;

int getid(int x){
    
    
    return lower_bound(v.begin(), v.end(), x) - v.begin() + 1;
}

int main(){
    
    
    int n = read();
    for (int i = 1; i <= n; ++i) {
    
    
        v.push_back(a[i] = read());
        v.push_back(b[i] = read());
    }
    sort(v.begin(), v.end());
    v.erase(unique(v.begin(), v.end()), v.end());
    for (int i = 1; i <= n; ++i) {
    
    
        a[i] = getid(a[i]);
        b[i] = getid(b[i]);
        diff[a[i]]++;
        diff[b[i]]--;
    }
    int sum = 0, res = 0;
    for (int i = 1; i < v.size(); ++i) {
    
    
        sum += diff[i];
        if (sum > 0) res += v[i] - v[i - 1];
    }
    printf("%d\n", res);
    return 0;
}