Different ways to add parentheses

Math String Dynamic Programming Recursion Memoization

73.1% acceptance

Jan 12, 2026

6314

398

Given a string expression of numbers and operators, return all possible results from computing all the different possible ways to group numbers and operators. You may return the answer in any order. The test cases are generated such that the output values fit in a 32-bit integer and the number of different results does not exceed 104.

Solution

Rust

Time O(n³)

Space O(n)

LeetCode

solution.rs

impl Solution {
  pub fn diff_ways_to_compute(expression: String) -> Vec<i32> {
    let mut result = Vec::new();
    
    for (i, ch) in expression.chars().enumerate() {
      if ch == '+' || ch == '-' || ch == '*' {
        let left = Self::diff_ways_to_compute(expression[..i].to_string());
        let right = Self::diff_ways_to_compute(expression[i+1..].to_string());
        
        for &l in &left {
          for &r in &right {
            match ch {
              '+' => result.push(l + r),
              '-' => result.push(l - r),
              '*' => result.push(l * r),
              _ => {}
            }
          }
        }
      }
    }
    
    if result.is_empty() {
      result.push(expression.parse().unwrap());
    }
    
    result
  }
}