hdu 5338 線段樹+stl+貪心

標籤：

下午比賽的時候寫搓了，晚上重寫一次就過了，o(╯□╰)o。

思路：按照字典序貪心，用線段樹來維護區間最值，用set來維護求出答案的封閉區間。

  1 #include <algorithm>  2 #include <iostream>  3 #include <cstring>  4 #include <cstdio>  5 #include <cmath>  6 #include <set>  7 using namespace std;  8   9 const int N = 100001; 10 int a[N]; 11 int pos[N]; 12 int ans[N]; 13 bool visit[N]; 14 set<int> s; 15 set<int>::iterator it; 16  17 struct Node 18 { 19     int l, r, maxn; 20 } node[N << 2]; 21  22 void pushup( int i ) 23 { 24     node[i].maxn = max( node[i << 1].maxn, node[i << 1 | 1].maxn ); 25 } 26  27 void build( int i, int l, int r ) 28 { 29     node[i].l = l, node[i].r = r; 30     if ( l == r ) 31     { 32         node[i].maxn = a[l]; 33         return ; 34     } 35     int mid = ( l + r ) >> 1; 36     build( i << 1, l, mid ); 37     build( i << 1 | 1, mid + 1, r ); 38     pushup(i); 39 } 40  41 void update( int i, int pos, int val ) 42 { 43     if ( node[i].l == pos && node[i].r == pos ) 44     { 45         node[i].maxn = val; 46         return ; 47     } 48     int mid = ( node[i].l + node[i].r ) >> 1; 49     if ( pos <= mid ) 50     { 51         update( i << 1, pos, val ); 52     } 53     else 54     { 55         update( i << 1 | 1, pos, val ); 56     } 57     pushup(i); 58 } 59  60 int query( int i, int l, int r ) 61 { 62     if ( node[i].l == l && node[i].r == r ) 63     { 64         return node[i].maxn; 65     } 66     int mid = ( node[i].l + node[i].r ) >> 1; 67     if ( r <= mid ) 68     { 69         return query( i << 1, l, r ); 70     } 71     else if ( l > mid ) 72     { 73         return query( i << 1 | 1, l, r ); 74     } 75     else 76     { 77         return max( query( i << 1, l, mid ), query( i << 1 | 1, mid + 1, r ) ); 78     } 79 } 80  81 int main () 82 { 83     int t; 84     scanf("%d", &t); 85     while ( t-- ) 86     { 87         int n; 88         scanf("%d", &n); 89         for ( int i = 1; i <= n; i++ ) 90         { 91             scanf("%d", &a[i]); 92             pos[a[i]] = i; 93         } 94         memset( ans, -1, sizeof(ans) ); 95         memset( visit, 0, sizeof(visit) ); 96         build( 1, 1, n ); 97         s.clear(); 98         for ( int i = 1; i <= n; i++ ) 99         {100             if ( ans[i] != -1 ) continue;101             int start = 1;102             if ( !s.empty() )103             {104                 it = s.upper_bound(pos[i]);105                 if ( it != s.begin() )106                 {107                     it--;108                     start = (*it);109                     start++;110                 }111             }112             int tmp = query( 1, start, pos[i] );113             if ( pos[i] != n && !visit[a[pos[i] + 1]] && tmp < a[pos[i] + 1] )114             {115                 ans[i] = a[pos[i] + 1];116                 update( 1, pos[i] + 1, -1 );117             }118             else119             {120                 ans[i] = tmp;121                 visit[tmp] = true;122                 for ( int j = pos[tmp]; j < pos[i]; j++ )123                 {124                     ans[a[j]] = a[j + 1];125                 }126                 s.insert(pos[i]);127             }128         }129         for ( int i = 1; i < n; i++ )130         {131             printf("%d ", ans[i]);132         }133         printf("%d\n", ans[n]);134     }135     return 0;136 }

 

hdu 5338 線段樹+stl+貪心