Welcome back! This lesson will focus on advanced string manipulation in Go. String manipulation is a vital skill for solving real-world programming challenges. Gaining proficiency in these techniques will enable you to decompose complex problems into simpler ones and improve your adaptability when working within different programming languages or contexts.

Let's explore a common coding interview challenge: finding the longest common starting sequence of characters (prefix) shared among a slice of strings. Given a slice of strings such as {"flower", "flow", "flight"}, the longest common prefix is "fl".

Our strategy for solving this problem in Go is:

1. Check for Empty Input: If the input slice is empty, the function will return an empty string as there's nothing to compare.
2. Identify the Shortest String: To optimize the comparison, find the shortest string, which limits the number of comparisons needed in subsequent steps.
3. Character by Character Comparison: Compare characters of the shortest string with corresponding characters in all other strings.
   • For each character index, store the character for reference.
   • Traverse all strings in the slice to check for character matches at each index. If any mismatch is detected, return the substring from the start up to (but excluding) that index.
4. Return the Shortest String: If no mismatch occurs, the function returns the shortest string as the longest common prefix.

For example, given the input {"flower", "flow", "flight"}:

1. The slice is not empty.
2. The function identifies "flow" as the shortest.
3. Start comparing each character of "flow" with the others:
   • At index 0, all strings have 'f'.
   • At index 1, all strings have 'l'.
   • At index 2, "flower" and "flow" have 'o', but "flight" has 'i', leading to a mismatch.
4. A mismatch at index 2 results in returning the substring "fl".

Here's how to implement this algorithm in Go:

Go
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1package main
2
3import (
4    "fmt"
5)
6
7func longestCommonPrefix(strs []string) string {
8    if len(strs) == 0 {
9        return ""
10    }
11    
12    shortest := strs[0]
13    for _, str := range strs {
14        if len(str) < len(shortest) {
15            shortest = str
16        }
17    }
18
19    for i := 0; i < len(shortest); i++ {
20        charToCheck := shortest[i]
21        for _, str := range strs {
22            if i >= len(str) || str[i] != charToCheck {
23                return shortest[:i]
24            }
25        }
26    }
27    return shortest
28}
29
30func main() {
31    strs := []string{"flower", "flow", "flight"}
32    fmt.Println(longestCommonPrefix(strs)) // Outputs: "fl"
33}

Let's break down the longestCommonPrefix function step by step:

Function Definition

This line declares the function longestCommonPrefix, which returns a string and accepts a slice of strings:

Go
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1func longestCommonPrefix(strs []string) string

Check for Empty Input

This line checks if the input slice is empty, returning an empty string if true since no common prefix can be determined:

Go
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1if len(strs) == 0 {
2    return ""
3}

Identify the Shortest String

Initially, set shortest to the first string in the slice. Iterate through the slice to find the string with the smallest length, reducing the number of comparisons needed later:

Go
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1shortest := strs[0]
2for _, str := range strs {
3    if len(str) < len(shortest) {
4        shortest = str
5    }
6}

Character by Character Comparison

This loop evaluates each character index of the shortest string. For each index, it stores the character in charToCheck:

Go
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1for i := 0; i < len(shortest); i++ {
2    charToCheck := shortest[i]

Inner Loop for Comparison

The internal loop checks if the character at the current index in each string matches charToCheck. On finding a mismatch, it returns the substring from the start up to (but excluding) that index:

Go
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1for _, str := range strs {
2    if i >= len(str) || str[i] != charToCheck {
3        return shortest[:i]
4    }
5}

Return the Shortest String

If no mismatch is detected, the function returns shortest as it represents the longest common prefix:

Go
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1return shortest

In future lessons, we'll continue exploring various string manipulation techniques essential for solving diverse algorithmic challenges. Our focus remains on helping you develop a comprehensive understanding rather than relying on memorization. Keep practicing, and let's dive deeper into mastering strings in Go!