题目:
Given two binary strings, return their sum (also a binary string).
For example,
a = "11"
b = "1"
Return "100"
.
题解:
二进制加法都是从最低位(从右加到左)。所以对两个字符串要从最后一位开始加,如果遇见长度不一的情况,就把短的字符串高位补0.
每轮计算要加上进位,最后跳出循环后要坚持进位是否为1,以便更新结果。
代码如下(from discussion):
1 public String addBinary(String a, String b) {
2 int m = a.length();
3 int n = b.length();
4 int carry = 0;
5 String res = "";
6 // the final length of the result depends on the bigger length between a and b,
7 // (also the value of carry, if carry = 1, add "1" at the head of result, otherwise)
8 int maxLen = Math.max(m, n);
9 for (int i = 0; i < maxLen; i++) {
// start from last char of a and b
// notice that left side is int and right side is char
// so we need to minus the decimal value of '0'
int p=0,q=0;
if(i<m)
p = a.charAt(m-1-i) - '0';
else
p = 0;
if(i<n)
q = b.charAt(n-1-i)-'0';
else
q = 0;
int tmp = p + q + carry;
carry = tmp / 2;
res += tmp % 2;
}
return (carry == 0) ? res : "1" + res;
}