【RMQ】POJ 2452

#define N 50010int a[N];int max(int i,int j){return a[i]>a[j]?i:j;}int min(int i,int j){return a[i]>a[j]?j:i;}int dp1[20][N];//dp[i][j]表示從j開始，長度為2^i區間最大值(最小值)int dp2[20][N];int n,m;void init_rmq(){    int i,j;    for(i=1;i<=n;i++){        dp1[0][i] = i;        dp2[0][i] = i;    }    int t = floor(log((double)n)/log(2.0));//向下取整    for(i=1;i<=t;i++){        for(j=1;j+(1<<(i-1))<=n;j++){            dp1[i][j] = max(dp1[i-1][j],dp1[i-1][j+(1<<(i-1))]);            dp2[i][j] = min(dp2[i-1][j],dp2[i-1][j+(1<<(i-1))]);        }    }}int rmq(int l,int r,int s){    int k = floor(log((r-l+1)*1.0)/log(2.0));    if(s==1){        return max(dp1[k][l],dp1[k][r-(1<<k)+1]);    } else return min(dp2[k][l],dp2[k][r-(1<<k)+1]);}int gao(int x){    int l = 1,r = x-1,mid;    while(l<r){        mid = (l+r)>>1;        if(a[rmq(mid,r,1)]<a[x])r = mid-1;        else l = mid+1;    }    return rmq(l,x,2);}int main(){FRE;    while(scanf("%d",&n) != -1){        int i,j;        for(i=1;i<=n;i++){            scanf("%d",&a[i]);        }        init_rmq();        int ans = 0;        for(i=1;i<=n;i++){            int t = i-gao(i);            if(ans<t)ans = t;        }        if(ans<1)ans=-1;        printf("%d\n",ans);    }    return 0;}