Problem Overview & Intuition

Iteratively construct the sequence starting from "1". For each transition, run-length encode consecutive identical digits into [count, digit], producing the next term in the sequence.

Step-by-Step Approach

1. Initialize curr = "1".
2. Iterate i from 2 to n.
3. Traverse curr using two pointers or a loop counting contiguous duplicate characters.
4. Append count + char to next.
5. Update curr = next.
6. Return curr.

Optimal Implementation (JavaScript)

function countAndSay(n) {
  let curr = '1';
  for (let i = 2; i <= n; i++) {
    let next = '', j = 0;
    while (j < curr.length) {
      let count = 1;
      while (j + 1 < curr.length && curr[j] === curr[j + 1]) {
        count++;
        j++;
      }
      next += count + curr[j];
      j++;
    }
    curr = next;
  }
  return curr;
}

Complexity Analysis