Easy python (O(NlogN)

#1 
def solve(self, arr):
    arr.sort() 
    n = len(arr) 
      
    for i in range(n - 1): 
          
        if arr[i] == arr[i + 1]: 
            continue
        if arr[i] == n - i - 1: 
            return 1
      
    if arr[n - 1] == 0: 
        return 1 
    return -1