Merge adjacent equal elements

Array Stack Simulation

42.0% acceptance

Mar 16, 2026

You are given an integer array nums. You must repeatedly apply the following merge operation until no more changes can be made: If any two adjacent elements are equal, choose the leftmost such adjacent pair in the current array and replace them with a single element equal to their sum. After each merge operation, the array size decreases by 1. Repeat the process on the updated array until no more changes can be made. Return the final array after all possible merge operations.

Solution

Rust

Time O(n²)

Space O(n)

LeetCode

solution.rs

impl Solution {
  pub fn merge_adjacent(nums: Vec<i32>) -> Vec<i64> {
    // Use a stack-based approach: push elements one by one.
    // After pushing, if top two are equal, merge them (and keep merging while top two are equal).
    let mut stack: Vec<i64> = Vec::new();

    for &num in &nums {
      stack.push(num as i64);
      // Merge while last two elements are equal
      while stack.len() >= 2 {
        let len = stack.len();
        if stack[len - 1] == stack[len - 2] {
          let val = stack.pop().unwrap();
          *stack.last_mut().unwrap() = val * 2;
        } else {
          break;
        }
      }
    }

    stack
  }
}