Why Intervals Are a Common Problem Pattern in DSA C - Test Your Knowledge

Practice - 5 Tasks

1fill in blank

easy

Complete the code to declare a struct for an interval with start and end.

DSA C

typedef struct {
    int start;
    int [1];
} Interval;

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Avalue

Blength

Cend

Drange

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'length' instead of 'end' for the second member.

The struct for an interval typically has 'start' and 'end' to mark boundaries.

2fill in blank

medium

Complete the code to check if two intervals overlap.

DSA C

int isOverlap(Interval a, Interval b) {
    return !(a.end <= b.[1] || b.end <= a.start);
}

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Avalue

Bstart

Clength

Drange

Attempts:

3 left

💡 Hint

Common Mistakes

Comparing with 'length' or 'value' which are not interval boundaries.

To check overlap, compare the end of one with the start of the other.

3fill in blank

hard

Fix the error in the function that merges two overlapping intervals.

DSA C

Interval mergeIntervals(Interval a, Interval b) {
    Interval merged;
    merged.start = a.start < b.start ? a.start : b.[1];
    merged.end = a.end > b.end ? a.end : b.end;
    return merged;
}

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Astart

Brange

Cvalue

Dlength

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'end' or 'length' instead of 'start' for the minimum start.

When merging, the start is the minimum of both starts.

4fill in blank

hard

Fill both blanks to create a function that sorts intervals by their start time.

DSA C

int compareIntervals(const void *a, const void *b) {
    Interval *i1 = (Interval *)[1];
    Interval *i2 = (Interval *)[2];
    return i1->start - i2->start;
}

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Aa

Bb

Cstart

Dend

Attempts:

3 left

💡 Hint

Common Mistakes

Using 'start' or 'end' as variable names instead of 'a' and 'b'.

In qsort compare function, cast the void pointers to Interval pointers using 'a' and 'b'.

5fill in blank

hard

Fill all three blanks to create a function that merges a list of intervals.

DSA C

int mergeAllIntervals(Interval intervals[], int n, Interval result[]) {
    if (n == 0) return 0;
    qsort(intervals, n, sizeof(Interval), compareIntervals);
    int idx = 0;
    result[idx] = intervals[0];
    for (int i = 1; i < n; i++) {
        if (result[idx].end >= intervals[i].[1]) {
            if (result[idx].end < intervals[i].[2]) {
                result[idx].end = intervals[i].[3];
            }
        } else {
            idx++;
            result[idx] = intervals[i];
        }
    }
    return idx + 1;
}

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Astart

Bend

Attempts:

3 left

💡 Hint

Common Mistakes

Mixing up start and end in comparisons and assignments.

The function merges intervals by checking if current interval's start is within the last merged interval's end, then updates the end if needed.