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#3918
Medium Algorithms

Sum of primes between number and its reverse

75.5% acceptance
May 13, 2026
25
2
You are given an integer n. Let r be the integer formed by reversing the digits of n. Return the sum of all prime numbers between min(n, r) and max(n, r), inclusive.

Solution

Rust
Time O(n²)
Space O(1)
LeetCode
solution.rs
impl Solution {
  pub fn sum_of_primes_in_range(n: i32) -> i32 {
    let mut r = 0i32;
    let mut x = n;
    while x > 0 {
      r = r * 10 + x % 10;
      x /= 10;
    }
    let lo = n.min(r);
    let hi = n.max(r);
    let mut sum = 0i32;
    for v in lo..=hi {
      if v < 2 { continue; }
      let mut prime = true;
      let mut d = 2;
      while d * d <= v {
        if v % d == 0 { prime = false; break; }
        d += 1;
      }
      if prime { sum += v; }
    }
    sum
  }
}