蓝桥杯 排序题目

题目链接:

https://www.lanqiao.cn/problems/20097/learning/?page=1&first_category_id=1

思路:

容易想到不可能超过2次.所以只需倒序判断何处出现错排,然后将其校正,在此之后如果仍然出现错排,ans+=2即可.

代码:

#include<bits/stdc++.h>
using namespace std;
 
inline int read() {
    int ans = 0, f = 1;
    char ch = getchar();
    while (ch < '0' || ch > '9') {
        if (ch == '-')f = -1;
        ch = getchar();
    }
    while (ch <= '9' && ch >= '0') {
        ans = ans * 10 + ch - '0';
        ch = getchar();
    }
    return ans * f;
}
const int N = 2e5+10;
int a[N],b[N],c[N];
int main() {
    int n =read();
    for (int i =1; i<= n; i++) {
        a[i] = read();
        b[i] = a[i];
    }
    sort(b+1,b+1+n);
    int ans =0;
    for (int i = n; i>= 2; i--) {
        if (b[i] == a[i]) {
            continue;
        }
        if (!ans)
        {
            ans+=i;
            int offset = 0;
            for (int j = i; j>=1; j--) {
                if (b[i] == a[j]) {
                    offset = i - j;
                    break;
                }
            }
 
            for (int j = 1; j<= i; j++) {
                c[(j + offset-1) % i + 1] = a[j];
            }
            for (int j = 1; j<= i; j++) {
                a[j] = c[j];
            }
        }
        else {
            ans += 2;
            break;
        }
 
    }
    cout<<ans;
    return 0;