Codeforces Round #609 (Div. 2) C. Long Beautiful Integer

链接：

https://codeforces.com/contest/1269/problem/C

题意：

You are given an integer x of n digits a1,a2,…,an, which make up its decimal notation in order from left to right.

Also, you are given a positive integer k<n.

Let's call integer b1,b2,…,bm beautiful if bi=bi+k for each i, such that 1≤i≤m−k.

You need to find the smallest beautiful integer y, such that y≥x.

思路：

记录前k个，模拟比大小，要修改值的时候从后往前选第一个不是9的字符修改，同时把9修改为0

代码：

#include<bits/stdc++.h>
using namespace std;
const int MAXN = 2e5+10;

int n, k;
char num[MAXN], ans[MAXN];

bool Check()
{
    for (int i = k;i < n;i++)
    {
        if (num[i] < ans[i%k])
            return true;
        if (num[i] > ans[i%k])
            return false;
    }
    return true;
}

int main()
{
    scanf("%d%d", &n, &k);
    scanf("%s", num);
    for (int i = 0;i < k;i++)
        ans[i] = num[i];
    ans[k] = 0;
    if (Check())
    {
        printf("%d\n", n);
        for (int i = 0;i < n;i++)
            printf("%c", ans[i%k]);
        printf("\n");
        return 0;
    }
    for (int i = k-1;i >= 0;i--)
    {
        if (ans[i] != '9')
        {
            ans[i]++;
            break;
        }
        else
            ans[i] = '0';
    }
    printf("%d\n", n);
    for (int i = 0;i < n;i++)
        printf("%c", ans[i%k]);
    printf("\n");

    return 0;
}