Codeforces 452F

哈希学到不好。。。
假如，a+c=2*b
对于比b小的数左高位右低位求hash
对于比b小的数低高位右高位求hash
当两个hash值完全一样就gg掉

#include <iostream>#include <cstdio>#include <string>#include <cstring>#include <algorithm>#include <set>#include <map>#include <vector>#include <stack>#include <cmath>#include <cassert>#include <bitset>using namespace std;typedef __int64 LL;typedef unsigned __int64 ULL;const int N = 300005;int n , a[N];ULL MAGIC = 3 , power[N];struct stree {    ULL Hl , Hr;}t[N << 1];inline int id(int l , int r) {return l + r | l != r;}#define MID int mid = l + r >> 1#define Left l , mid#define Right mid + 1 , rinline void pushup(int p , int l , int mid , int r) {    int L = id(Left) , R = id(Right);    t[p].Hl = t[L].Hl * power[r - mid] + t[R].Hl;    t[p].Hr = t[R].Hr * power[mid - l + 1] + t[L].Hr;}void update(int l , int r , int x , int w) {    int p = id(l , r);    if (l == r) {        t[p].Hl = t[p].Hr = w + 1;        return;    } MID;    if (x <= mid)        update(Left , x , w);    else        update(Right , x , w);    pushup(p , l , mid , r);}ULL gethashl(int l , int r , int top , int bot) {    int p = id(l , r);    if (top <= l && r <= bot)        return t[p].Hl;    MID;    if (bot <= mid)        return gethashl(Left , top , bot);    else if (top > mid)        return gethashl(Right , top , bot);    else        return gethashl(Left , top , mid) * power[bot - mid] + gethashl(Right , mid + 1 , bot);}ULL gethashr(int l , int r , int top , int bot) {    int p = id(l , r);    if (top <= l && r <= bot)        return t[p].Hr;    MID;    if (bot <= mid)        return gethashr(Left , top , bot);    else if (top > mid)        return gethashr(Right , top , bot);    else        return gethashr(Right , mid + 1 , bot) * power[mid - top + 1] + gethashr(Left , top , mid);}#define mid (l+r)/2void query(int l,int r){    int p=id(l,r);    printf("%llu %llu %d %d %d\n",t[p].Hl,t[p].Hr,l,r,p);    if(l==r){        return ;    }    query(l,mid);    query(mid+1,r);}void work() {    int i , x , y;    scanf("%d",&n) ;    for(int i=1;i<=n;i++)scanf("%d",&a[i]);    power[0] = 1;    for(int i=1;i<=n;i++)power[i]=power[i-1]*MAGIC;    for (i = 1 ; i <= n ; ++ i) {        update(1 , n , i , 0);    }    //query(1,n);    for (i = 1 ; i <= n ; ++ i) {        x = min(a[i] - 1 , n - a[i]);        //[a[i] - x , a[i] - 1]        //[a[i] + 1 , a[i] + x]        if (x && gethashl(1 , n , a[i] - x , a[i] - 1) != gethashr(1 , n , a[i] + 1 , a[i] + x)) {            puts("YES");            return;        }         update(1 , n , a[i] , 1);    }    puts("NO");}int main(){    #ifdef DouBi    freopen("in.cpp","r",stdin);    #endif // DouBi    work();    return 0;}