[Luogu] 被污染的河流

#include <iostream>
#include <cstdio>
#include <algorithm>

#define gc getchar()

using std:: sort;
using std:: cout;
using std:: min;
using std:: max;
const int N = 10100;

int n, js;
int X[N << 2], W[N << 4], F[N << 4];
struct Node {int x_1, x_2, h, how;} lp[N << 1];

inline int read() {
    int x = 0; char c = gc;
    while(c < ‘0‘ || c > ‘9‘) c = gc;
    while(c >= ‘0‘ && c <= ‘9‘) x = x * 10 + c - ‘0‘, c = gc;
    return x;
}

inline void Add(int _x_1, int _y_1, int _x_2, int _y_2) {
    if(_y_1 == _y_2) {
        int _1 = _x_1, _2 = _x_2;
        _x_1 = min(_1, _2); _x_2 = max(_1, _2);
        lp[++ js].x_1 = _x_1; lp[js].x_2 = _x_2; lp[js].h = _y_1 - 1; lp[js].how = 1; X[js] = _x_1;
        lp[++ js].x_1 = _x_1; lp[js].x_2 = _x_2; lp[js].h = _y_1 + 1; lp[js].how = -1; X[js] = _x_2;
    } else {
        int _1 = _y_1, _2 = _y_2;
        _y_1 = min(_1, _2); _y_2 = max(_1, _2);
        lp[++ js].x_1 = _x_1 - 1; lp[js].x_2 = _x_1 + 1; lp[js].h = _y_1; lp[js].how = 1; X[js] = _x_1 - 1;
        lp[++ js].x_1 = _x_1 - 1; lp[js].x_2 = _x_1 + 1; lp[js].h = _y_2; lp[js].how = -1; X[js] = _x_1 + 1;
    }
}

inline bool cmp(Node a, Node b) {return a.h < b.h;}

int Find(int num, int r_) {
    int L = 1, R = r_, ret;
    while(L <= R) {
        int Mid = (L + R) >> 1;
        if(X[Mid] <= num) L = Mid + 1, ret = Mid;
        else R = Mid - 1;
    }
    return ret;
}

#define lson jd << 1
#define rson jd << 1 | 1

void Pushup(int jd, int l, int r) {
    if(F[jd]) W[jd] = X[r + 1] - X[l];
    else if(l == r) W[jd] = 0;
    else W[jd] = W[lson] + W[rson];
}

void Sec_G(int l, int r, int jd, int x, int y, int how) {
    if(x <= l && r <= y) {F[jd] += how; Pushup(jd, l, r); return ;}
    int mid = (l + r) >> 1;
    if(x <= mid) Sec_G(l, mid, lson, x, y, how);
    if(y > mid)  Sec_G(mid + 1, r, rson, x, y, how);
    Pushup(jd, l, r);
}

int main() {
    n = read();
    for(int i = 1; i <= n; i ++) {
        int x_1 = read(), y_1 = read(), x_2 = read(), y_2 = read();
        Add(x_1, y_1, x_2, y_2);
    }
    sort(X + 1, X + js + 1);
    sort(lp + 1, lp + js + 1, cmp);
    int k = 1;
    for(int i = 2; i <= js; i ++) if(X[i] != X[i + 1]) X[++ k] = X[i];
    long long Answer = 0;
    for(int i = 1; i < js; i ++) {
        int l = Find(lp[i].x_1, k), r = Find(lp[i].x_2, k) - 1;
        Sec_G(1, k - 1, 1, l, r, lp[i].how);
        Answer += W[1] * (lp[i + 1].h - lp[i].h);
    }
    cout << Answer;
    return 0;
}