LeetCode #2194 — EASY

Cells in a Range on an Excel Sheet

Build confidence with an intuition-first walkthrough focused on core interview patterns fundamentals.

The Problem

Problem Statement

A cell (r, c) of an excel sheet is represented as a string "<col><row>" where:

<col> denotes the column number c of the cell. It is represented by alphabetical letters.
- For example, the 1^st column is denoted by 'A', the 2^nd by 'B', the 3^rd by 'C', and so on.
<row> is the row number r of the cell. The r^th row is represented by the integer r.

You are given a string s in the format "<col1><row1>:<col2><row2>", where <col1> represents the column c1, <row1> represents the row r1, <col2> represents the column c2, and <row2> represents the row r2, such that r1 <= r2 and c1 <= c2.

Return the list of cells (x, y) such that r1 <= x <= r2 and c1 <= y <= c2. The cells should be represented as strings in the format mentioned above and be sorted in non-decreasing order first by columns and then by rows.

Example 1:

Input: s = "K1:L2"
Output: ["K1","K2","L1","L2"]
Explanation:
The above diagram shows the cells which should be present in the list.
The red arrows denote the order in which the cells should be presented.

Example 2:

Input: s = "A1:F1"
Output: ["A1","B1","C1","D1","E1","F1"]
Explanation:
The above diagram shows the cells which should be present in the list.
The red arrow denotes the order in which the cells should be presented.

Constraints:

s.length == 5
'A' <= s[0] <= s[3] <= 'Z'
'1' <= s[1] <= s[4] <= '9'
s consists of uppercase English letters, digits and ':'.

Step 01

Brute Force Baseline

Problem summary: A cell (r, c) of an excel sheet is represented as a string "<col><row>" where: <col> denotes the column number c of the cell. It is represented by alphabetical letters. For example, the 1st column is denoted by 'A', the 2nd by 'B', the 3rd by 'C', and so on. <row> is the row number r of the cell. The rth row is represented by the integer r. You are given a string s in the format "<col1><row1>:<col2><row2>", where <col1> represents the column c1, <row1> represents the row r1, <col2> represents the column c2, and <row2> represents the row r2, such that r1 <= r2 and c1 <= c2. Return the list of cells (x, y) such that r1 <= x <= r2 and c1 <= y <= c2. The cells should be represented as strings in the format mentioned above and be sorted in non-decreasing order first by columns and then by rows.

Baseline thinking

Start with the most direct exhaustive search. That gives a correctness anchor before optimizing.

Pattern signal: General problem-solving

Example 1

"K1:L2"

Example 2

"A1:F1"

Core Insight

What unlocks the optimal approach

From the given string, find the corresponding rows and columns.
Iterate through the columns in ascending order and for each column, iterate through the rows in ascending order to obtain the required cells in sorted order.

Interview move: turn each hint into an invariant you can check after every iteration/recursion step.

Step 03

Algorithm Walkthrough

Iteration Checklist

Define state (indices, window, stack, map, DP cell, or recursion frame).
Apply one transition step and update the invariant.
Record answer candidate when condition is met.
Continue until all input is consumed.

Use the first example testcase as your mental trace to verify each transition.

Step 04

Edge Cases

Minimum Input

Single element / shortest valid input

Validate boundary behavior before entering the main loop or recursion.

Duplicates & Repeats

Repeated values / repeated states

Decide whether duplicates should be merged, skipped, or counted explicitly.

Extreme Constraints

Upper-end input sizes

Re-check complexity target against constraints to avoid time-limit issues.

Invalid / Corner Shape

Empty collections, zeros, or disconnected structures

Handle special-case structure before the core algorithm path.

Step 05

Full Annotated Code

Source-backed implementations are provided below for direct study and interview prep.

// Accepted solution for LeetCode #2194: Cells in a Range on an Excel Sheet
class Solution {
    public List<String> cellsInRange(String s) {
        List<String> ans = new ArrayList<>();
        for (char i = s.charAt(0); i <= s.charAt(3); ++i) {
            for (char j = s.charAt(1); j <= s.charAt(4); ++j) {
                ans.add(i + "" + j);
            }
        }
        return ans;
    }
}

// Accepted solution for LeetCode #2194: Cells in a Range on an Excel Sheet
func cellsInRange(s string) (ans []string) {
	for i := s[0]; i <= s[3]; i++ {
		for j := s[1]; j <= s[4]; j++ {
			ans = append(ans, string(i)+string(j))
		}
	}
	return
}

# Accepted solution for LeetCode #2194: Cells in a Range on an Excel Sheet
class Solution:
    def cellsInRange(self, s: str) -> List[str]:
        return [
            chr(i) + str(j)
            for i in range(ord(s[0]), ord(s[-2]) + 1)
            for j in range(int(s[1]), int(s[-1]) + 1)
        ]

// Accepted solution for LeetCode #2194: Cells in a Range on an Excel Sheet
/**
 * [2194] Cells in a Range on an Excel Sheet
 *
 * A cell (r, c) of an excel sheet is represented as a string "<col><row>" where:
 *
 * 	<col> denotes the column number c of the cell. It is represented by alphabetical letters.
 *
 * 		For example, the 1^st column is denoted by 'A', the 2^nd by 'B', the 3^rd by 'C', and so on.
 *
 *
 * 	<row> is the row number r of the cell. The r^th row is represented by the integer r.
 *
 * You are given a string s in the format "<col1><row1>:<col2><row2>", where <col1> represents the column c1, <row1> represents the row r1, <col2> represents the column c2, and <row2> represents the row r2, such that r1 <= r2 and c1 <= c2.
 * Return the list of cells (x, y) such that r1 <= x <= r2 and c1 <= y <= c2. The cells should be represented as strings in the format mentioned above and be sorted in non-decreasing order first by columns and then by rows.
 *  
 * Example 1:
 * <img alt="" src="https://assets.leetcode.com/uploads/2022/02/08/ex1drawio.png" style="width: 250px; height: 160px;" />
 * Input: s = "K1:L2"
 * Output: ["K1","K2","L1","L2"]
 * Explanation:
 * The above diagram shows the cells which should be present in the list.
 * The red arrows denote the order in which the cells should be presented.
 *
 * Example 2:
 * <img alt="" src="https://assets.leetcode.com/uploads/2022/02/09/exam2drawio.png" style="width: 500px; height: 50px;" />
 * Input: s = "A1:F1"
 * Output: ["A1","B1","C1","D1","E1","F1"]
 * Explanation:
 * The above diagram shows the cells which should be present in the list.
 * The red arrow denotes the order in which the cells should be presented.
 *
 *  
 * Constraints:
 *
 * 	s.length == 5
 * 	'A' <= s[0] <= s[3] <= 'Z'
 * 	'1' <= s[1] <= s[4] <= '9'
 * 	s consists of uppercase English letters, digits and ':'.
 *
 */
pub struct Solution {}

// problem: https://leetcode.com/problems/cells-in-a-range-on-an-excel-sheet/
// discuss: https://leetcode.com/problems/cells-in-a-range-on-an-excel-sheet/discuss/?currentPage=1&orderBy=most_votes&query=

// submission codes start here

impl Solution {
    pub fn cells_in_range(s: String) -> Vec<String> {
        let s = s.as_bytes();
        (s[0]..=s[3])
            .flat_map(|col| (s[1]..=s[4]).map(move |row| format!("{}{}", col as char, row as char)))
            .collect::<Vec<_>>()
    }
}

// submission codes end

#[cfg(test)]
mod tests {
    use super::*;

    #[test]
    fn test_2194_example_1() {
        let s = "K1:L2".to_string();

        let result = vec_string!["K1", "K2", "L1", "L2"];

        assert_eq!(Solution::cells_in_range(s), result);
    }

    #[test]
    fn test_2194_example_2() {
        let s = "A1:F1".to_string();

        let result = vec_string!["A1", "B1", "C1", "D1", "E1", "F1"];

        assert_eq!(Solution::cells_in_range(s), result);
    }
}

// Accepted solution for LeetCode #2194: Cells in a Range on an Excel Sheet
function cellsInRange(s: string): string[] {
    const ans: string[] = [];
    for (let i = s.charCodeAt(0); i <= s.charCodeAt(3); ++i) {
        for (let j = s.charCodeAt(1); j <= s.charCodeAt(4); ++j) {
            ans.push(String.fromCharCode(i) + String.fromCharCode(j));
        }
    }
    return ans;
}

Step 06

Interactive Study Demo

Use this to step through a reusable interview workflow for this problem.

Custom checkpoints (one per line)

Press Step or Run All to begin.

Step 07

Complexity Analysis

Time

O(m × n)

Space

O(m × n)

Approach Breakdown

BRUTE FORCE

O(n²) time

O(1) space

Two nested loops check every pair or subarray. The outer loop fixes a starting point, the inner loop extends or searches. For n elements this gives up to n²/2 operations. No extra space, but the quadratic time is prohibitive for large inputs.

OPTIMIZED

O(n) time

O(1) space

Most array problems have an O(n²) brute force (nested loops) and an O(n) optimal (single pass with clever state tracking). The key is identifying what information to maintain as you scan: a running max, a prefix sum, a hash map of seen values, or two pointers.

Shortcut: If you are using nested loops on an array, there is almost always an O(n) solution. Look for the right auxiliary state.

Coach Notes

Common Mistakes

Review these before coding to avoid predictable interview regressions.

Off-by-one on range boundaries

Wrong move: Loop endpoints miss first/last candidate.

Usually fails on: Fails on minimal arrays and exact-boundary answers.

Fix: Re-derive loops from inclusive/exclusive ranges before coding.