题解 | 字符串操作

def replace_str(s, replace_key):
    l, r, c1, c2 = replace_key.split()
    l, r = int(l)-1, int(r)-1 # 转换为索引
    s = s[: l] + s[l: r+1].replace(c1, c2) + s[r+1:] # 对指定范围内的字符串切片替换并拼接
    return s

n, m = map(int, input().split())
s = input()
for i in range(m):
    s = replace_str(s, input())
print(s)