CodeForces Round #305 (div1) B. Mike and Feet （單調棧）

題目

本Markdown編輯器使用[StackEdit][6]修改而來，用它寫博客，將會帶來全新的體驗哦：

B - Mike and Feet
Time Limit:1000MS Memory Limit:262144KB 64bit IO Format:%I64d & %I64u
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Status
Description
Mike is the president of country What-The-Fatherland. There are n bears living in this country besides Mike. All of them are standing in a line and they are numbered from 1 to n from left to right. i-th bear is exactly ai feet high.

A group of bears is a non-empty contiguous segment of the line. The size of a group is the number of bears in that group. The strength of a group is the minimum height of the bear in that group.

Mike is a curious to know for each x such that 1 ≤ x ≤ n the maximum strength among all groups of size x.

Input
The first line of input contains integer n (1 ≤ n ≤ 2 × 105), the number of bears.

The second line contains n integers separated by space, a1, a2, …, an (1 ≤ ai ≤ 109), heights of bears.

Output
Print n integers in one line. For each x from 1 to n, print the maximum strength among all groups of size x.

Sample Input
Input
10
1 2 3 4 5 4 3 2 1 6
Output
6 4 4 3 3 2 2 1 1 1

看了一個題解才明白：下面鏈接
這裏寫鏈接內容

一開始從頭推暴力寫法，利用線段書的思想一層層更新取最大值，果斷超時了，後來從答案出發想解題

#include<cstdio>
#include<iostream>
#define INT_MAX 2147483647
using namespace std;

int n;
int a[200005];
int l[200005],r[200005];
int ans[200005];
int main(){
    cin>>n;
    for(int i=1;i<=n;i++)
    scanf("%d",&a[i]);
    a[0]=a[n+1]-INT_MAX;
    for(int i=1;i<=n;i++){
        int j=i-1;
        while(a[j]>=a[i])j=l[j];//跳躍更新//j--;
        l[i]=j;
    }
    for(int i=n;i>0;i--){
        int j=i+1;
        while(a[j]>=a[i])j=r[j];
        r[i]=j;
    }
    for(int i=1;i<=n;i++){
        int d=r[i]-l[i]-1;
        if(a[i]>ans[d])ans[d]=a[i];
    }
    for(int i=n;i>1;i--){
        if(ans[i]>ans[i-1])ans[i-1]=ans[i];
    }
   for(int i=1;i<=n;i++){
    printf("%d ",ans[i]);
   }
    return 0;
}

恩，後續補一波單調棧，希望自己能記得