[POJ1117] Picture && 线段树+扫描线

来源：互联网发布：格罗兹尼巷战知乎编辑：程序博客网时间：2024/05/22 02:28
把边排序从左往右进行扫描计算周长注意排序时左边的边要排在右边的边的前面
#include<cstdio>#include<algorithm>#include<cstring>#include<iostream>#define SF scanf#define PF printf#define ls (i*2)#define rs (i*2+1)using namespace std;const int MAXN = 5000;struct Line {    int x, y1, y2;    bool GetIn;    Line () {}    Line(int _x, int _y, int __y, bool ok) : x(_x), y1(_y), y2(__y), GetIn(ok) {}    bool operator < (const Line &t) const {        return (x < t.x || (( x == t.x) && (GetIn && !t.GetIn)));    }};Line L[MAXN*2+10];int y[MAXN*2+10];struct Node {    int l, r, cnt, Seg, sum;    bool L_ok, R_ok;};struct Seg_Tree {    Node tree[MAXN * 4 + 10];    void build(int i, int l, int r) {        int mid = (l + r) >> 1;        tree[i].l = l; tree[i].r = r;        tree[i].Seg = tree[i].cnt = tree[i].sum = 0;        tree[i].L_ok = tree[i].R_ok = false;        if(l == r-1) return ;        build(ls, l, mid);        build(rs, mid, r);    }    void update(int i) {        if(tree[i].cnt) {            tree[i].L_ok = tree[i].R_ok = true;            tree[i].Seg = 1;            tree[i].sum = y[tree[i].r] - y[tree[i].l];        }        else {            if(tree[i].l == tree[i].r - 1) {                tree[i].L_ok = tree[i].R_ok = false;                tree[i].Seg = 0;                tree[i].sum = 0;            }            else {                tree[i].L_ok = tree[ls].L_ok;                tree[i].R_ok = tree[rs].R_ok;                tree[i].Seg = tree[ls].Seg + tree[rs].Seg;                if(tree[ls].R_ok && tree[rs].L_ok) tree[i].Seg--;                tree[i].sum = tree[ls].sum + tree[rs].sum;            }        }    }    void insert(int i, int l, int r, bool f) {        if(r < tree[i].l || tree[i].r <= l) return ;        if(l <= tree[i].l && tree[i].r <= r) {            tree[i].cnt += (f ? 1 : -1);            update(i);            return ;        }        insert(ls, l, r, f);        insert(rs, l, r, f);        update(i);    }} seg;int main(){    int n;    while(~SF("%d", &n)) {        for(int i = 1; i <= n; i++) {            int x1, x2, y1, y2;            SF("%d%d%d%d", &x1, &y1, &x2, &y2);            y[i*2-1] = y1; y[i*2] = y2;            L[i*2-1] = Line(x1, y1, y2, true);            L[i*2] = Line(x2, y1, y2, false);        }        sort(y+1, y+1+2*n);        sort(L+1, L+1+2*n);        int N = unique(y+1, y+1+2*n) - (y+1);        seg.build(1, 1, N);        int Len = 0, ans = 0;        for(int i = 1; i <= 2*n; i++) {            int pos1 = lower_bound(y+1, y+1+N, L[i].y1) - y;            int pos2 = lower_bound(y+1, y+1+N, L[i].y2) - y;            seg.insert(1, pos1, pos2, L[i].GetIn);            ans += abs(Len - seg.tree[1].sum);            ans += seg.tree[1].Seg * 2 * (L[i+1].x - L[i].x);            Len = seg.tree[1].sum;        }        printf("%d\n" , ans);    }}
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