luogu P1502 窗口的星星

题目链接

P1502 窗口的星星

题解

扫描线+线段树

线段树的每一个节点处理的是左边框放在当前x-1位置时的框内星星的亮度大小

按照x坐标进行离散化，得到离散化后每一个坐标x的可影响的范围

维护扫描线，扫到可以加某颗星星就把星星加进去，扫到该出来的时候就把星星搞出来,线段树维护一下

代码

#include<cstdio>
#include<cstring>
#include<algorithm>

const int maxn = 100007; 

int n,w,h;
int pou[maxn << 2],T[maxn << 2],tag[maxn << 2]; 

struct P {
    int x,y,l,k,ymax,id;
}star[maxn << 2];
inline bool cmp1(P a,P b) { return a.y < b.y; }
inline bool cmp2(P a,P b) { if(a.id == b.id) return a.k < b.k; return a.id < b.id; }
inline bool cmp3(P a,P b) { if(a.x == b.x) return a.k < b.k; return a.x < b.x;  }
void pushdown(int x,int l,int r) {
    if(!tag[x]) return;
    if(l == r) { tag[x] = 0; return; }
    int mid = l + r >> 1;
    tag[x << 1] += tag[x]; tag[x << 1 | 1] += tag[x];
    T[x << 1] += tag[x];  T[x << 1 | 1]+=tag[x];
    tag[x] = 0;
} 

void modify(int x,int l,int r,int tl,int tr,int val){
    pushdown(x,l,r);
    if(tl <= l && r <= tr) {
        tag[x] = val; T[x] += val;
        return;
    }
    int mid = (l + r) >> 1;
    if(tl <= mid) modify(x << 1,l,mid,tl,tr,val);
    if(mid < tr) modify(x << 1 | 1,mid + 1,r,tl,tr,val);
    T[x] = std::max(T[x << 1],T[x << 1 | 1]);
}
void init() {
    memset(T,0,sizeof(T));
    memset(tag,0,sizeof(tag));
    scanf("%d%d%d",&n,&w,&h);
    for(int x,y,l,i = 1;i <= n ;++ i) {
        scanf("%d%d%d",&x,&y,&l);
        star[i] = (P) {x, y, l, 1};
        star[i + n] = (P){ x + w - 1, y, -l, 2};
        star[i + (n << 1)].y = y + h - 1;
        star[i + (n << 1)].k = 3;
        star[i].id = star[i + n].id = star[i + (n << 1)].id = i;
    }
}  

void solve() {
    std::sort(star + 1,star + n * 3 + 1,cmp1);
    int cnt = 0;
    for(int i = 1;i <= n * 3;++ i) pou[i] = star[i].y;
    for(int i = 1;i <= n * 3;++ i)
        if(star[i].y == pou[i - 1]) star[i].y = star[i - 1].y;
        	else star[i].y =++ cnt;
    std::sort(star + 1,star + n * 3 + 1,cmp2);
    for(int i = 1;i <= n * 3;i += 3) star[i].ymax = star[i + 1].ymax = star[i + 2].y;
    for(int i = 3;i <= n << 1;++ i)  star[i] = star[i + ((i - 1) >> 1)];
    std::sort(star + 1,star + (n << 1) + 1,cmp3);
    int ans = 0;
    for(int i = 1;i <= n << 1;++ i) {
        modify(1,0,cnt,star[i].y,star[i].ymax,star[i].l);
        ans = std::max(ans,T[1]);
    }
    printf("%d\n",ans);
    return ;
}
int main() {
    int t; scanf("%d",&t);
    while(t --) {
    	init();
        solve();
    }
    return 0;
}