题解 | 字符串操作

n, m = map(int, input().split())
s = input()
# 直接按照题目要求写代码
for i in range(m):
    shuru = input().split()
    l, r, c1, c2 = shuru[0], shuru[1], shuru[2], shuru[3]
    l, r = int(l) - 1, int(r) - 1
    s = s[0:l] + s[l : r + 1].replace(c1, c2) + s[r + 1 :]
print(s)