ABC107&ARC101 Candles 思维

9276: Candles

时间限制: 1 Sec  内存限制: 128 MB
提交: 70  解决: 34
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题目描述

There are N candles placed on a number line. The i-th candle from the left is placed on coordinate xi. Here, x1<x2<…<xN holds.
Initially, no candles are burning. Snuke decides to light K of the N candles.
Now, he is at coordinate 0. He can move left and right along the line with speed 1. He can also light a candle when he is at the same position as the candle, in negligible time.
Find the minimum time required to light K candles.
Constraints
1≤N≤105
1≤K≤N
xi is an integer.
|xi|≤108
x1<x2<…<xN

输入

Input is given from Standard Input in the following format:

N K
x1 x2 … xN

输出

Print the minimum time required to light K candles.

样例输入

复制样例数据

5 3
-30 -10 10 20 50

样例输出

40

提示

He should move and light candles as follows:

• Move from coordinate 0 to −10.
• Light the second candle from the left.
• Move from coordinate −10 to 10.
• Light the third candle from the left.
• Move from coordinate 10 to 20.
• Light the fourth candle from the left.

来源/分类

ABC107&ARC101

 题意很好理解，就是在数轴上的n个点选出k个，计算出最小距离

写的时候想了很多奇奇怪怪的想法，但都不太在点上

网上搜题解看到一个很朴素的做法

只有1e5的点，循环一遍也不会t，那么就从最左边的点开始每k个计算一次距离，求出最小的即可

代码：

#include <bits/stdc++.h>

using namespace std;
const int maxn = 1e5 + 10;
typedef long long ll;
ll a[maxn];
ll ans=1e18;
int main() {
    int n,k;
    scanf("%d%d",&n,&k);
    for(int i=1; i<=n; i++)
        cin>>a[i];
    int l;
    int r;
    for(int i=1; i+k-1<=n; i++){
        l=i,r=i+k-1;
        ans=min(ans,a[r]-a[l]+min(abs(a[l]),abs(a[r])));
    }
    cout<<ans<<endl;
    return 0;
}