15、二进制求和

给定两个二进制字符串，返回他们的和（用二进制表示）。

输入为非空字符串且只包含数字 1 和 0。

示例 1:

输入: a = “11”, b = “1”
输出: “100”
示例 2:

输入: a = “1010”, b = “1011”
输出: “10101”

我的代码

class Solution {
    public String addBinary(String a, String b) {
        StringBuilder  sum = new StringBuilder();
		int i = a.length()-1;
		int j = b.length()-1;
		int div= 0;
		int k;
		if(i >= j){
			k = j;
		}else {
			k = i;
		}
		while (k >= 0) {
			int a1 = Integer.parseInt(Character.toString(a.charAt(i--)));
		//	System.out.println("a1   "+a1);
			int b1 = Integer.parseInt(Character.toString(b.charAt(j--)));
		//	System.out.println("b1   "+b1);
			if(a1+b1+div == 3 ){
				div = 1;
				sum.append("1");
			}else if (a1+b1+div ==2 ) {
				div = 1;
				sum.append("0");
			}else {
				int x = a1 + b1 + div;
				sum.append(Integer.toBinaryString(x));
				div = 0;
			}
			k--;
		}
		i = a.length();
	    j = b.length();
		if( i == j){
			return (div == 1)?sum.append("1").reverse().toString():
				sum.reverse().toString();
		}
		
		if(i < j){
			int k1 = j - i;
			while (k1 > 0) {
				int b2 = Integer.parseInt(Character.toString(b.charAt(k1-1)));
				if ( b2+div ==2 ) {
					div = 1;
					sum.append("0");
				}else {
					int x1 = b2+ div;
					sum.append(Integer.toBinaryString(x1));
					div = 0;
				}
				k1--;
			}
			
			if(div == 1){
				sum.append("1");
				return sum.reverse().toString();
			}else {
				return sum.reverse().toString();
			}
		}else {
			int k2 = i - j;
		//	System.out.println("k2   "+k2);
			while (k2 > 0) {
			//	System.out.println("div  "+ div);
				int b2 = Integer.parseInt(Character.toString(a.charAt(k2-1)));
				if ( b2+div ==2 ) {	
					div = 1;
					sum.append("0");
				}else {
					int x1 = b2+ div;
					sum.append(Integer.toBinaryString(x1));
					div = 0;
				}
				k2--;
			}
			
			if(div == 1){
				sum.append("1");
				return sum.reverse().toString();
			}else {
				return sum.reverse().toString();
			}
		}
    }
}

排名靠前的Java代码

class Solution {
     public String addBinary(String a, String b) {
            char[] aArray = a.toCharArray();
            char[] bArray = b.toCharArray();
            if(aArray.length>=bArray.length){
                return addBinary(aArray,bArray);
            }
            return addBinary(bArray,aArray);
        }
 
        public String addBinary(char[] aArray,char[] bArray){
            int target = 0;
            int initIndex = aArray.length-bArray.length;
            for(int i = bArray.length-1;i>=0;i--){
                int temp = (int)aArray[initIndex+i]+(int)bArray[i]+ target - (int)'0';
                if(temp>'1'){
                    aArray[initIndex+i] = (char)(temp - 2);
                    target = 1;
                }else {
                    aArray[initIndex+i] = (char)temp;
                    target = 0;
                }
            }
            if(target == 0){
                return String.valueOf(aArray);
            }
            for(int i = initIndex - 1;i>=0;i--){
                if(aArray[i]=='0'){
                    aArray[i]++;
                    return String.valueOf(aArray);
                }
                aArray[i]--;
            }
            return "1"+String.valueOf(aArray);
        }
}