AcWing 792. 高精度减法

java:

好难呜呜呜呜

import java.util.*;
public class Main {
	// 判断是否有 A >= B
    public static boolean cmp(List A, List B) {
        if (A.size() != B.size()) return A.size() > B.size();
        for (int i = A.size() - 1; i >= 0; i--) {
            if (A.get(i) != B.get(i)) return A.get(i) > B.get(i);
        }
        return true;
    }
    
    public static List sub(List A, List B) {
        List C = new ArrayList();
        
        int t = 0; // 差
        for (int i = 0; i < A.size(); i++) {
            t += A.get(i);
            if (i < B.size()) t -= B.get(i);
            C.add((t + 10) % 10); // t >= 0: t; t < 0 : t + 10(借位)
            if (t < 0) t = -1;
            else t = 0;
        }
        while(C.size() > 1 && C.get(C.size() - 1) == 0) C.remove(C.size() - 1); // 删除前导0
        
        return C;
    }
    
    public static void main(String[] args) {
        Scanner scan = new Scanner(System.in);
        String a = scan.nextLine();
        String b = scan.nextLine();
        
        List A = new ArrayList(), B = new ArrayList();
        for (int i = a.length() - 1; i >= 0; i--) A.add(a.charAt(i) - '0');
        for (int i = b.length() - 1; i >= 0; i--) B.add(b.charAt(i) - '0');
        
        if (cmp(A, B)) {
            List C = sub(A, B);
            for (int i = C.size() - 1; i >= 0; i--) System.out.print(C.get(i));
        }
        else {
            System.out.print("-");
            List C = sub(B, A);
            for (int i = C.size() - 1; i >= 0; i--) System.out.print(C.get(i));
        }
    }
}