题解 | 字符串操作

n, m = map(int, input().split(" "))
s = input()
for _ in range(m):
    l, r, c1, c2 = input().split(" ")
    s = s[: int(l) - 1] + s[int(l) - 1 : int(r)].replace(c1, c2) + s[int(r) :]
print(s)