Count Words with Given Prefix in DSA C++ - Interactive Practice

Practice - 5 Tasks

1fill in blank

easy

Complete the code to check if a word starts with the given prefix.

DSA C++

bool startsWith(const string& word, const string& prefix) {
    return word.[1](0, prefix.size()) == prefix;
}

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Areplace

Bfind

Ccompare

Dsubstr

Attempts:

3 left

💡 Hint

Common Mistakes

Using find instead of substr returns the position, not the substring.

Using compare returns an int, not a string.

The substr function extracts a substring from the word starting at index 0 with length equal to prefix size, which is then compared to the prefix.

2fill in blank

medium

Complete the code to count how many words start with the given prefix.

DSA C++

int countPrefix(const vector<string>& words, const string& prefix) {
    int count = 0;
    for (const auto& word : words) {
        if (word.size() >= prefix.size() && word.[1](0, prefix.size()) == prefix) {
            count++;
        }
    }
    return count;
}

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Areplace

Bfind

Csubstr

Dcompare

Attempts:

3 left

💡 Hint

Common Mistakes

Using find returns position, which is not suitable for prefix check.

Using compare returns int, not string.

Using substr to extract the prefix part of each word allows comparison with the given prefix to count matches.

3fill in blank

hard

Fix the error in the code to correctly count words starting with the prefix.

DSA C++

int countPrefix(const vector<string>& words, const string& prefix) {
    int count = 0;
    for (const auto& word : words) {
        if (word.size() >= prefix.size() && word.[1](0, prefix.size(), prefix) == 0) {
            count++;
        }
    }
    return count;
}

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Acompare

Bsubstr

Cfind

Dreplace

Attempts:

3 left

💡 Hint

Common Mistakes

Using find returns position, not 0 for match.

Using substr returns string, cannot be compared to 0.

The compare function can compare the prefix with the start of the word and returns 0 if they match.

4fill in blank

hard

Fill both blanks to create a map of prefix counts for given words.

DSA C++

unordered_map<string, int> prefixCount(const vector<string>& words, int prefixLen) {
    unordered_map<string, int> counts;
    for (const auto& word : words) {
        if (word.size() >= [1]) {
            string prefix = word.[2](0, prefixLen);
            counts[prefix]++;
        }
    }
    return counts;
}

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AprefixLen

Bword.size()

Csubstr

Dfind

Attempts:

3 left

💡 Hint

Common Mistakes

Using find instead of substr to extract prefix.

Checking word.size() < prefixLen instead of >=.

Check if word length is at least prefixLen, then extract prefix using substr from index 0 with length prefixLen.

5fill in blank

hard

Fill all three blanks to return the count of words starting with prefix using a loop and condition.

DSA C++

int countWordsWithPrefix(const vector<string>& words, const string& prefix) {
    int count = 0;
    for (const auto& [1] : words) {
        if ([2].[3](0, prefix.size()) == prefix) {
            count++;
        }
    }
    return count;
}

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Aword

Bwords

Csubstr

Dfind

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'words' as loop variable instead of 'word'.

Using find instead of substr for prefix extraction.

Use 'word' as loop variable, then call word.substr(0, prefix.size()) to compare with prefix.