【LeetCode】Plus One && 【九度】题目1198：a+b

Plus One 
Total Accepted: 4206 Total Submissions: 14127 My Submissions
Given a number represented as an array of digits, plus one to the number.
题目意思为给定一个数组，这个数组内的数代表某个大数，也就是可能为100位甚至多少位的一个数。
例如123456789012345678901234567890000，那么digits的每个位必然为一个个位数。
两个大数相加，可以使用数组，按位累加。
大于10就进位，同时将当前位-1，并且上一位加1。
Java AC

public class Solution {
    public int[] plusOne(int[] digits) {
        int len = digits.length;
		int addNum[] = new int[len + 1];
		addNum[len] = 1;
		for (int i = len - 1; i >= 0; i--) {
			addNum[i + 1] += digits[i];
			if (addNum[i + 1] >= 10) {
				addNum[i + 1] -= 10;
				addNum[i] += 1;
			}
		}
		if (addNum[0] ==  0) {
			System.arraycopy(addNum, 1, digits, 0, len);
			return digits;
		}else {
			return addNum;
		}
    }
}

LeetCode Add Binary 也是大数相加，只不过这次是二进制，知道进制相加的原则即可。
Java AC

public class Solution {
    public String addBinary(String a, String b) {
        if(a == null || b == null){
            return "";
        }
        if("".equals(a) || "".equals(b)){
            return "";
        }
        if("".equals(a.replaceAll("0", "")) && "".equals(b.replaceAll("0", ""))){
        	return "0";
        }
        int len1 = a.length();
        int len2 = b.length();
        char arrayA[] = a.toCharArray();
        char arrayB[] = b.toCharArray();
        int maxLen = Math.max(len1,len2);
        int minLen = Math.min(len1,len2);
        int array[] = new int[maxLen+1];
        int k = maxLen;
        if(maxLen == len1){
            for(int i = minLen-1; i >= 0; i--){
                array[k] += arrayA[k-1] - '0' + arrayB[i] - '0';
                if(array[k] >= 2){
                    array[k] -= 2;
                    array[k-1] += 1;
                }
                k--;
            }
            while(k > 0){
                array[k] += arrayA[k-1] - '0';
                if(array[k] >= 2){
                    array[k] -= 2;
                    array[k-1] += 1;
                }
                k--;
            }
        }else{
            for(int i = minLen-1; i >= 0; i--){
                array[k] += arrayA[i] - '0' + arrayB[k-1] - '0';
                if(array[k] >= 2){
                    array[k] -= 2;
                    array[k-1] += 1;
                }
                k--;
            }
            while(k > 0){
                array[k] += arrayB[k-1] - '0';
                if(array[k] >= 2){
                    array[k] -= 2;
                    array[k-1] += 1;
                }
                k--;
            }
        }
        StringBuffer sb = new StringBuffer();
        int i = 0;
        if(array[0] == 0){
            i = 1;
        }
        for(; i < maxLen+1; i++){
            sb.append(array[i]);
        }
        return sb.toString();
    }
}

九度题目1198：a+b 2010年华中科技大学计算机研究生机试真题是一类题。
当时用了三种解法去解决。
一并给代码。
方法1 Java AC

import java.math.BigDecimal;
import java.util.Scanner;
public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        while(scanner.hasNext()){
            String a = scanner.next();
            String b = scanner.next(); 
            BigDecimal ad = new BigDecimal(a);
            BigDecimal bd = new BigDecimal(b);
            BigDecimal c = ad.add(bd);
            System.out.println(c);
        }
    }
}
/**************************************************************
    Problem: 1198
    User: wzqwsrf
    Language: Java
    Result: Accepted
    Time:980 ms
    Memory:84752 kb
****************************************************************/

方法2 Java AC

import java.util.Scanner;
public class Main {
    /*
     * 1198
     */
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        while(scanner.hasNext()){             
            String a = scanner.next();
            String b = scanner.next(); 
            int alength = a.length();
            int blength = b.length();
            int minlength = Math.min(alength, blength);
            int maxlength = Math.max(alength, blength);
            int in = 0 ;
            String result = "";
            String maxStr = alength>blength?a:b;
            String minStr = alength<blength?a:b;
            int c = maxlength-minlength;
            for (int i = minlength -1; i >= 0; i--) {
                int sa = minStr.charAt(i)-'0';
                int sb = maxStr.charAt(c + i)-'0';
                int count = sa+sb+in;
                if(count >= 10){
                    in = 1;
                    result = count-10+result;
                }else{
                    in = 0 ;
                    result = count + result;
                }                 
            }             
            for (int i = c-1 ; i >= 0 ; i--) {
                int max = maxStr.charAt(i)-'0';
                int count = max+in;
                if(count>=10){
                    in = 1;
                    result = count-10+result;
                }else{
                    in = 0 ;
                    result = count + result;
                }
            }
            if(in==1){
                result = in +result ;
            }
            System.out.println(result);
        }
    }
}
/**************************************************************
    Problem: 1198
    User: wzqwsrf
    Language: Java
    Result: Accepted
    Time:1120 ms
    Memory:210296 kb
****************************************************************/

方法3 Java AC

import java.util.Scanner;
public class Main {
    public static void main(String[] args) {
        Scanner scanner = new Scanner(System.in);
        while(scanner.hasNext()){
            String a = scanner.next();
            String b = scanner.next();
            int aLength = a.length();
            int bLength = b.length();
            int max = Math.max(aLength, bLength);
            int[] arrayA = new int[max+1];
            int[] arrayB = new int[max+1];
            int k = 0;
            for (int i = max+1-aLength ; i< max+1; i++ ) {
                arrayA[i] = a.charAt(k)-'0';
                k++;
            }
            k = 0;
            for (int i = max+1-bLength ; i< max+1; i++ ) {
                arrayB[i] = b.charAt(k)-'0';
                k++;
            }
            int[] arrayC = new int[max+1];
             
            for (int i = max ; i> 0 ;i--) {
                arrayC[i] += arrayA[i] + arrayB[i];
                if (arrayC[i]>=10) {
                    arrayC[i] -= 10;
                    arrayC[i-1] += 1;
                }
            }
            if (arrayC[0] == 0) {
                for (int i = 1; i < arrayC.length; i++) {
                    System.out.print(arrayC[i]);
                }
                System.out.println();
            }else {
                for (int i = 0; i < arrayC.length; i++) {
                    System.out.print(arrayC[i]);
                }
                System.out.println();
            }
        }
    }
}
/**************************************************************
    Problem: 1198
    User: wzqwsrf
    Language: Java
    Result: Accepted
    Time:2290 ms
    Memory:95360 kb
****************************************************************/