题解 | 茶杯和球

import sys

def solve():
    data = sys.stdin.read().split()
    ptr = 0
    n = int(data[ptr])
    x = int(data[ptr+1])
    k = int(data[ptr+2])

    ptr += 3
    for _ in range(k):     
        a = int(data[ptr])
        ptr += 1
        b = int(data[ptr])
        ptr += 1
        if a == x:
            x = b
            continue
        elif b == x:
            x = a      
    print(x)
solve()