备战百度笔试

排序后，双指针移动比较，大的就赋值即可：

import java.util.*;
public class Main{
    public static void main(String[] args) {
        Scanner sc = new Scanner(System.in);
        StringBuilder r = new StringBuilder(sc.nextLine());
        String str = sc.nextLine();
        char[] v = new char[str.length()];
        for(int i = 0; i < str.length(); ++i){
            v[i] = str.charAt(i);
        }
        Arrays.sort(v);
        int i = v.length - 1, j = 0;
        while(i >= 0 && j < r.length()){
            if(r.charAt(j) < v[i]){
                r.setCharAt(j, v[i]);
                j++;
                i--;
            }else j++;
        }
        System.out.println(r);
    }
}