Fraction addition and subtraction

Math String Simulation

66.4% acceptance

Jan 13, 2026

891

696

Given a string expression representing an expression of fraction addition and subtraction, return the calculation result in string format. The final result should be an irreducible fraction. If your final result is an integer, change it to the format of a fraction that has a denominator 1. So in this case, 2 should be converted to 2/1.

Solution

Rust

Time O(n²)

Space O(n)

LeetCode

solution.rs

impl Solution {
  pub fn fraction_addition(expression: String) -> String {
    fn gcd(a: i64, b: i64) -> i64 { if b == 0 { a } else { gcd(b, a % b) } }
    let expr = expression.as_bytes();
    let n = expr.len();
    let mut num = 0i64; let mut den = 1i64;
    let mut i = 0usize;
    while i < n {
      let sign = if expr[i] == b'-' { i += 1; -1i64 } else { if expr[i] == b'+' { i += 1; } 1i64 };
      let mut a = 0i64;
      while i < n && expr[i].is_ascii_digit() { a = a * 10 + (expr[i] - b'0') as i64; i += 1; }
      a *= sign;
      i += 1; // skip '/'
      let mut b = 0i64;
      while i < n && expr[i].is_ascii_digit() { b = b * 10 + (expr[i] - b'0') as i64; i += 1; }
      num = num * b + a * den;
      den = den * b;
      let g = gcd(num.abs(), den.abs());
      num /= g; den /= g;
    }
    format!("{}/{}", num, den)
  }
}