Excel BI - Excel Challenge 869

🔰 Extract a strictly increasing sequence of integers from this string, reading from left to right.

Illustration for Excel BI - Excel Challenge 869

Challenge Description

🔰 Extract a strictly increasing sequence of integers from this string, reading from left to right. Start from the first digit. Use the minimum number of consecutive digits required to form a number strictly greater than the previous one. If the remaining digits at the end of the string cannot form a number strictly greater than the last extracted number, ignore them.

Solutions

R Solution

library(tidyverse)
library(readxl)

path <- "Excel/800-899/869/869 Extract nums.xlsx"
input <- read_excel(path, range = "A1:A100")
test <- read_excel(path, range = "B1:B100")

extract_inc_seq_simple <- function(s) {
  digits <- as.numeric(strsplit(s, "")[[1]])
  result <- numeric(0)
  last_num <- -Inf
  i <- 1

  while (i <= length(digits)) {
    found <- FALSE
    for (j in i:length(digits)) {
      candidate <- as.numeric(paste(digits[i:j], collapse = ""))
      if (candidate > last_num) {
        result <- c(result, candidate)
        last_num <- candidate
        i <- j + 1
        found <- TRUE
        break
      }
    }
    if (!found) break
  }

  return(paste(result, collapse = ", "))
}

result <- input %>%
  mutate(Extracted = map_chr(Data, extract_inc_seq_simple))

all(result$Extracted == test$`Answer Expected`)
# [1] TRUE

R Analysis

• Logic: Read the workbook ranges needed for the challenge; Derive the required intermediate columns; Iterate through the sequence until the rule is satisfied.
• Strengths: The algorithm is explicit about the sequence rule, so the control flow is easy to validate against the prompt.
• Areas for Improvement: The solution assumes the workbook layout and selected ranges remain stable, so any structural change in the sheet would require small adjustments.
• Gem: The non-obvious part is the local rule inside the loop, because that rule determines the whole output.

Python Solution

import pandas as pd

path = "Excel/800-899/869/869 Extract nums.xlsx"
input_df = pd.read_excel(path, usecols="A", nrows=100)
test_df = pd.read_excel(path, usecols="B", nrows=100)

def extract_inc_seq_simple(s):
    digits = [int(ch) for ch in str(s)]
    result = []
    last_num = float('-inf')
    i = 0
    n = len(digits)
    while i < n:
        found = False
        for j in range(i, n):
            candidate = int(''.join(str(d) for d in digits[i:j+1]))
            if candidate > last_num:
                result.append(candidate)
                last_num = candidate
                i = j + 1
                found = True
                break
        if not found:
            break
    return ', '.join(str(x) for x in result)

input_df['Extracted'] = input_df.iloc[:, 0].apply(extract_inc_seq_simple)

print(all(input_df['Extracted'] == test_df.iloc[:, 0]))

Python

The Python version keeps the algorithm explicit, which helps when the challenge depends on a greedy or iterative rule.

Difficulty Level

Medium / Hard

The challenge relies on a non-obvious iterative rule rather than a single straight aggregation.

Related Challenges

• Excel Challenge 870
• Excel Challenge 871
• Excel Challenge 872