题解 | 字符串操作

import java.util.Scanner;

// 注意类名必须为 Main, 不要有任何 package xxx 信息
public class Main {
    public static void main(String[] args) {
        Scanner in = new Scanner(System.in);
        int n = in.nextInt();
        int m = in.nextInt();
        in.nextLine();
        String s = in.nextLine();
        while(m-- > 0) {
            String[] line = in.nextLine().split(" ");
            
            int l = Integer.parseInt(line[0]);
            int r = Integer.parseInt(line[1]);
            char c1 = line[2].charAt(0);
            char c2 = line[3].charAt(0);

            s = replace(s, l, r, c1, c2);
        }
        System.out.print(s);
    }

    public static String replace(String s, int l, int r, char c1, char c2) {
        StringBuilder sb = new StringBuilder(s);
        for (int i = l - 1; i < r; i++) {
            if (sb.charAt(i) == c1) {
                sb.setCharAt(i, c2);
            }
        }
        return sb.toString();
    }
}