D - へんてこ辞書

• Time : $O(n)$
• Space : $O(n)$

python

N,A=map(int,input().split())
K=input()
K=int(K)
arr = list(map(int,input().split()))
 
def solve(A, now, k):
    vis = [0] * N
    id = 1
    while k > 0:
        if vis[now] > 0:
            cycle = id - vis[now]
            if cycle == 0:
                return now + 1
            k %= cycle
            if(k == 0):
                return now + 1
        else:
            vis[now] = id
            id = id + 1
        now = A[now] - 1
        k -= 1
    return now + 1

print(solve(arr, A - 1, K))