Poj2528-Mayor's posters-line segment tree discretization, basis

A. n (n <= 10000) Posters with a height of 1 byte are pasted on a board with a height of 1 byte and a length of byte. The posters are posted in order to show the scope of each poster, and find the number of posters that can be viewed at the end (incomplete ).

Idea: Because the array cannot be as large as 10 ^ 7, and the number of posters is only 10000, the boundary value is up to 20000, So we discretization the coordinate value, here we use sort, unique, and lower_bound to perform binary search. In sort sorting, the number of elements in the array after unique deduplication is used to create a line segment tree. After that, the line segment tree is marked by the interval operation and lazy. The number of times that a line segment tree record is currently posted. The last spof queries indicate the number of posters that can be viewed. Here, a vis array is used to record the number.

 

AC code:

  1 #include <iostream>  2 #include <cstdio>  3 #include <algorithm>  4 #include <vector>  5 #include <cstring>  6 using namespace std;  7 #define lson l, m, rt<<1  8 #define rson m+1, r, rt<<1|1  9 #define maxn 20000 10 struct node 11 { 12     int l, r; 13 }; 14 int sgt[maxn<<2]; 15 vector<node> arr; 16 vector<int> sor; 17 int lazy[maxn<<2]; 18 bool vis[maxn]; 19 void input() 20 { 21     arr.clear(); 22     sor.clear(); 23     int n; scanf("%d", &n); 24     for(int i = 0; i < n; i++) { 25         node x; scanf("%d%d", &x.l, &x.r); 26         arr.push_back(x); 27         sor.push_back(x.l); 28         sor.push_back(x.r); 29     } 30     sort(sor.begin(), sor.end()); 31     vector<int>::iterator it; 32     it = unique(sor.begin(), sor.end()); 33     sor.resize(distance(sor.begin(), it)); 34     memset(vis, 0, sizeof(vis)); 35     memset(lazy, 0, sizeof(lazy)); 36 } 37 void push_down(int rt) 38 { 39     if(lazy[rt] != 0) { 40         lazy[rt<<1] = lazy[rt]; 41         lazy[rt<<1|1] = lazy[rt]; 42         sgt[rt<<1] = lazy[rt]; 43         sgt[rt<<1|1] = lazy[rt]; 44         lazy[rt] = 0; 45     } 46 } 47 void build(int l, int r, int rt) 48 { 49     lazy[rt] = 0; 50     if(l == r) { 51         sgt[rt] = 0; 52         return; 53     } 54     int m = (l+r)>>1; 55     build(lson); 56     build(rson); 57 } 58 void change(int l, int r, int rt, int L, int R, int del) 59 { 60     if(L <= l && r <= R) { 61         lazy[rt] = del; 62         sgt[rt] = del; 63         return; 64     } 65     push_down(rt); 66     int m = (l + r)>>1; 67     if( L <= m) change(lson, L, R, del); 68     if(m < R) change(rson, L, R, del); 69 } 70 void query(int l, int r, int rt) 71 { 72     if(l == r) { 73         vis[sgt[rt]] = 1; 74         return; 75     } 76     push_down(rt); 77     int m = (l+r)>>1; 78     query(lson); 79     query(rson); 80 } 81 void num() 82 { 83     int ans = 0; 84     int l = sor.size(); 85     for(int i = 1; i <= l; i++) { 86         if(vis[i] != 0) ans ++; 87     } 88     printf("%d\n", ans); 89 } 90  91 void work() 92 { 93     input(); 94     int n = sor.size(); 95     build(1, n, 1); 96     int len = arr.size(); 97     for(int i = 0; i < len; i++){ 98         int l = lower_bound(sor.begin(), sor.end(), arr[i].l) - sor.begin()+1; 99         int r = lower_bound(sor.begin(), sor.end(), arr[i].r) - sor.begin()+1;100         change(1, n, 1, l, r, i+1);101     }102     query(1, n, 1);103     num();104 }105 int main()106 {107     int t; scanf("%d", &t);108     while(t--) work();109     return 0;110 }

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Poj2528-Mayor's posters-line segment tree discretization, basis