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  • Mister B and PR Shifts——思维题

    题目

    Some time ago Mister B detected a strange signal from the space, which he started to study.

    After some transformation the signal turned out to be a permutation p of length n or its cyclic shift. For the further investigation Mister B need some basis, that's why he decided to choose cyclic shift of this permutation which has the minimum possible deviation.

    Let's define the deviation of a permutation (p) as .

    Find a cyclic shift of permutation (p) with minimum possible deviation. If there are multiple solutions, print any of them.

    Let's denote id (k (0 ≤ k < n)) of a cyclic shift of permutation (p) as the number of right shifts needed to reach this shift, for example:

    • (k = 0): shift (p_1, p_2, ... p_n),
    • (k = 1): shift (p_n, p_1, ... p_{n - 1}),
    • ...,
    • (k = n - 1): shift (p_2, p_3, ... p_n, p_1).

    Input

    First line contains single integer (n (2 ≤ n ≤ 10^6)) — the length of the permutation.

    The second line contains (n) space-separated integers (p_1, p_2, ..., p_n (1 ≤ p_i ≤ n)) — the elements of the permutation. It is guaranteed that all elements are distinct.

    Output

    Print two integers: the minimum deviation of cyclic shifts of permutation p and the id of such shift. If there are multiple solutions, print any of them.

    Examples

    Input 1

    3
    1 2 3
    

    Output 1

    0 0
    

    Input 2

    3
    2 3 1
    

    Output 2

    0 1
    

    Input 3

    3
    3 2 1
    

    Output 3

    2 1
    

    Note

    In the first sample test the given permutation p is the identity permutation, that's why its deviation equals to 0, the shift id equals to 0 as well.

    In the second sample test the deviation of p equals to 4, the deviation of the 1-st cyclic shift (1, 2, 3) equals to 0, the deviation of the 2-nd cyclic shift (3, 1, 2) equals to 4, the optimal is the 1-st cyclic shift.

    In the third sample test the deviation of p equals to 4, the deviation of the 1-st cyclic shift (1, 3, 2) equals to 2, the deviation of the 2-nd cyclic shift (2, 1, 3) also equals to 2, so the optimal are both 1-st and 2-nd cyclic shifts.

    题解

    解题思路

    暴力枚举的话时间复杂度是(n^2)的,对于1e6的数据一定是超时的

    (l)统计的是(a_i >= i)的数量
    (r)统计的是(a_i < i)的数量
    (s_i)统计(a_x - x == i)的数量
    每次循环都把最后一位拿到第一位,其他的向后推一位
    这样(l)就减去(s_i),(r)加上(s_i)

    代码

    #include <cstdio>
    #include <cmath>
    using namespace std;
    const int N = 2e6+5;
    int n, a[N], s[N], l, r, h;
    long long sum, ans;
    int main() {
        scanf("%d", &n);
        for(int i = 1; i <= n; i++) {
            scanf("%d", &a[i]);
            sum += abs(a[i] - i);
            if (a[i] >= i) l++, s[a[i]-i]++;
            else r++;
        }
        ans = sum; h = 0;
        for(int i = 0; i < n; i++) {
            l -= s[i]; r += s[i];
            sum += r - l - 1;
            sum += 2 * a[n-i] - n - 1;
            l++, r--;
            s[i+a[n-i]]++;
            if (ans > sum) ans = sum, h = i + 1;
        }
        printf("%lld %d", ans, h);
        return 0;
    }
    
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  • 原文地址:https://www.cnblogs.com/Z8875/p/12852713.html
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