69 lines
1.8 KiB
Rust
69 lines
1.8 KiB
Rust
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pub fn add_binary(a: String, b: String) -> String {
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// Pad the strings with leading zeroes so they're the same length.
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let (a, b) = (
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format!("{:0>1$}", a, b.len()),
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format!("{:0>1$}", b, a.len()),
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);
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let mut carry = false;
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let mut sum = String::new();
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// Create reversed iterators for both binary strings.
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let (mut a, mut b) = (a.chars().rev(), b.chars().rev());
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while let Some(a) = a.next() {
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// Safe to unwrap since we know both iterators will be the same length.
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let b = b.next().unwrap();
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match (a, b) {
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('1', '1') => {
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// For 1 + 1, if we need to carry it will be 01 + 01 -> 10 + 01 -> 11.
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// And otherwise it will be 01 + 01 -> 10, and carry next digit.
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if carry {
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sum.push('1');
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} else {
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sum.push('0');
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carry = true;
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}
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}
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// For 1 + 0 (and associatively 0 + 1), if we need to carry it's the same
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// as 01 + 01 -> 10. And keep the carry set.
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// And otherwise it will just be 01 + 00 -> 01.
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('1', '0') | ('0', '1') => {
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if carry {
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sum.push('0');
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} else {
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sum.push('1');
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}
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}
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// For 0 + 0, if we need to carry it results in 1 and otherwise 0.
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('0', '0') => {
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if carry {
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sum.push('1');
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carry = false;
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} else {
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sum.push('0');
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}
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}
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_ => unreachable!(),
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}
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}
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// And if the final digits required carrying, add the 1 here at the end.
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if carry {
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sum.push('1');
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}
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sum.chars().rev().collect()
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}
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#[test]
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fn test_add_binary() {
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assert_eq!(add_binary("11".to_string(), "1".to_string()), "100");
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assert_eq!(add_binary("1010".to_string(), "1011".to_string()), "10101");
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assert_eq!(add_binary("1111".to_string(), "1111".to_string()), "11110");
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}
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