hdu 4747 Mex (线段树)

hdu 4747 Mex (线段树)

不错的思维题，犀利的线段树。解题思路百度很多。。我那蹩脚的表达能力，就不误导大家了。

#include<stdio.h>
#include<string.h>
#include<algorithm>
#include<map>
#define ll long long
#define lson l , m , rt << 1
#define rson m + 1 , r , rt << 1 | 1
using namespace std ;

const int maxn = 222222 ;
map<int,int> mp ;
int col[maxn<<2] , b[maxn] , a[maxn] , mx[maxn<<2] ;
ll ans = 0 , sum[maxn<<2] ;
int nxt[maxn] ;

inline void push_up ( int rt ) {
    sum[rt] = sum[rt<<1] + sum[rt<<1|1] ;
    mx[rt] = mx[rt<<1|1] ;
}

void push_down ( int rt , int m ) {
    if ( col[rt] != -1 ) {
        int ls = rt << 1 , rs = rt << 1 | 1 ;
        mx[ls] = mx[rs] = col[ls] = col[rs] = col[rt] ;
        sum[ls] = (ll) col[ls] * ( m - ( m >> 1 ) ) ;
        sum[rs] = (ll) col[rs] * ( m >> 1 ) ;
        col[rt] = -1 ;
    }
}

void build ( int l , int r , int rt ) {
    col[rt] = -1 ;
    if ( l == r ) {
        mx[rt] = sum[rt] = b[l] ;
        return ;
    }
    int m = ( l + r ) >> 1 ;
    build ( lson ) ;
    build ( rson ) ;
    push_up ( rt ) ;
}

int find ( int l , int r , int rt , int v ) {
    if ( l == r ) return l ;
    push_down ( rt , r - l + 1 ) ;
    int m = ( l + r ) >> 1 ;
    if ( mx[rt<<1] >= v ) return find ( lson , v ) ;
    else return find ( rson , v ) ;
}

void update ( int a , int b , int c , int l , int r , int rt ) {
    if ( a <= l && r <= b ) {
        col[rt] = c ;
        sum[rt] = (ll) c * ( r - l + 1 ) ;
        mx[rt] = c ;
        return ;
    }
    push_down ( rt , r - l + 1 ) ;
    int m = ( l + r ) >> 1 ;
    if ( a <= m ) update ( a , b , c , lson ) ;
    if ( m < b ) update ( a , b , c , rson ) ;
    push_up ( rt ) ;
}

void update ( int a , int l , int r , int rt ) {
    if ( l == r ) {
        mx[rt] = -1 ;
        sum[rt] = 0 ;
        return ;
    }
    push_down ( rt , r - l + 1 ) ;
    int m = ( l + r ) >> 1 ;
    if ( a <= m ) update ( a , lson ) ;
    else update ( a , rson ) ;
    push_up ( rt ) ;
}

void solve ( int n ) {
    int i , j , k , l , r ;
    for ( i = 1 ; i <= n ; i ++ ) {
        ans += sum[1] ;
        update ( i , 1 , n , 1 ) ;
        r = nxt[i] ;
        if ( mx[1] < a[i] ) continue ;
        l = find ( 1 , n , 1 , a[i] ) ;
        if ( l <= r ) update ( l , r , a[i] , 1 , n , 1 ) ;
    }
}

int main () {
    int n , i , j , k ;
    while ( scanf ( "%d" , &n ) != EOF ) {
        if ( n == 0 ) break ;
        ans = 0 ;
        mp.clear () ;
        for ( i = 1 ; i <= n ; i ++ ) scanf ( "%d" , &a[i] ) ;
        mp[a[1]] = 1 ;
        if ( a[1] == 0 ) k = b[1] = 1 ;
        else k = b[1] = 0 ;
        for ( i = 2 ; i <= n ; i ++ ) {
            mp[a[i]] = 1 ;
            while ( mp[k] ) k ++ ;
            b[i] = k ;
        }
        mp.clear () ;
        for ( i = n ; i>= 1 ; i -- ) {
            if ( !mp[a[i]] ) nxt[i] = n ;
            else nxt[i] = mp[a[i]] - 1 ;
            mp[a[i]] = i ;
        }
        build ( 1 , n , 1 ) ;
        solve ( n ) ;
        printf ( "%I64d
" , ans ) ;
    }
    return 0 ;
}