暴力标记

#include <iostream>
using namespace std;
const int N = 110;
bool st[N][N];
int main(){
    int n;  cin >> n;
    for(int i = 0; i < n; i ++ ){
        int x1, y1, x2, y2; cin >> x1 >> y1 >> x2 >> y2;
        for(int j = x1; j < x2; j ++ ){
            for(int k = y1; k < y2; k ++ ) st[j][k] = true;
        }
    }
    int res = 0;
    for(int i = 0; i < N; i ++ ){
        for(int j = 0; j < N; j ++ ){
            if(st[i][j])    res ++ ;
        }
    }
    cout << res << endl;
    return 0;
}

差分

#include <iostream>
using namespace std;
const int N = 110;
int graph[N][N], s[N][N];
void insert(int x1, int y1, int x2, int y2){
    graph[x1][y1] ++ ;
    graph[x1][y2 + 1] -- ;
    graph[x2 + 1][y1] -- ;
    graph[x2 + 1][y2 + 1] ++;
}
int main(){
    int n;  cin >> n;
    while(n -- ){
        int x1, y1, x2, y2;
        scanf("%d%d%d%d", &x1, &y1, &x2, &y2);
        x1 ++ , y1 ++ ;
        insert(x1, y1, x2, y2);
    }
    int cnt  = 0;
    for(int i = 1; i < N; i ++ ){
        for(int j = 1; j < N; j ++ ){
            s[i][j] = s[i - 1][j] + s[i][j - 1] - s[i - 1][j - 1] + graph[i][j];
            if(s[i][j]) cnt ++ ;
        }
    }
    cout << cnt << endl;
    return 0;
}