Completed Design-1

[sarvanibaru]

No description provided.

[super30admin]

Strengths:

• The code for both problems is well-structured and readable, with comments explaining the approach.
• The MinStack solution is correctly implemented and efficient.

Areas for Improvement:

1. For the HashSet problem, the primary hash function should use modulo operation to ensure the index is within the range [0, primaryBuckets-1]. The current method using division may not distribute keys properly and could lead to index out of bounds for large keys.
2. The secondary hash function should use modulo for the primary hash and division for the secondary hash, as in the reference solution. This ensures that the secondary index is computed correctly.
3. The student's solution does not handle the edge case for key=1000000. When primary index is 0, the secondary array should be of size 1001 to accommodate secondary index 1000. Otherwise, for key=1000000, the secondary index would be 1000, which is beyond the array size of 1000.
4. Consider using meaningful variable names. For example, arr could be renamed to storage or buckets for clarity.

Suggested Correction for HashSet:

• Change getPrimaryHash to return key % primaryBuckets;
• Change getSecondaryHash to return key / secondaryBuckets; (with secondaryBuckets=1000)
• In the add method, when creating the secondary array for primary index 0, create an array of size 1001 instead of 1000.

Example corrected code snippet for MyHashSet:

class MyHashSet {
    boolean[][] storage;
    int primaryBuckets;
    int secondaryBuckets;

    public MyHashSet() {
        this.primaryBuckets = 1000;
        this.secondaryBuckets = 1000;
        this.storage = new boolean[primaryBuckets][];
    }

    private int getPrimaryHash(int key) {
        return key % primaryBuckets;
    }

    private int getSecondaryHash(int key) {
        return key / secondaryBuckets;
    }

    public void add(int key) {
        int primaryIndex = getPrimaryHash(key);
        if (storage[primaryIndex] == null) {
            if (primaryIndex == 0) {
                storage[primaryIndex] = new boolean[secondaryBuckets + 1];
            } else {
                storage[primaryIndex] = new boolean[secondaryBuckets];
            }
        }
        int secondaryIndex = getSecondaryHash(key);
        storage[primaryIndex][secondaryIndex] = true;
    }

    // remove and contains methods similarly adjusted
}

[sarvanibaru]

Strengths:

• The code for both problems is well-structured and readable, with comments explaining the approach.
• The MinStack solution is correctly implemented and efficient.

Areas for Improvement:

1. For the HashSet problem, the primary hash function should use modulo operation to ensure the index is within the range [0, primaryBuckets-1]. The current method using division may not distribute keys properly and could lead to index out of bounds for large keys.
2. The secondary hash function should use modulo for the primary hash and division for the secondary hash, as in the reference solution. This ensures that the secondary index is computed correctly.
3. The student's solution does not handle the edge case for key=1000000. When primary index is 0, the secondary array should be of size 1001 to accommodate secondary index 1000. Otherwise, for key=1000000, the secondary index would be 1000, which is beyond the array size of 1000.
4. Consider using meaningful variable names. For example, arr could be renamed to storage or buckets for clarity.

Suggested Correction for HashSet:

• Change getPrimaryHash to return key % primaryBuckets;
• Change getSecondaryHash to return key / secondaryBuckets; (with secondaryBuckets=1000)
• In the add method, when creating the secondary array for primary index 0, create an array of size 1001 instead of 1000.

Example corrected code snippet for MyHashSet:

class MyHashSet {
    boolean[][] storage;
    int primaryBuckets;
    int secondaryBuckets;

    public MyHashSet() {
        this.primaryBuckets = 1000;
        this.secondaryBuckets = 1000;
        this.storage = new boolean[primaryBuckets][];
    }

    private int getPrimaryHash(int key) {
        return key % primaryBuckets;
    }

    private int getSecondaryHash(int key) {
        return key / secondaryBuckets;
    }

    public void add(int key) {
        int primaryIndex = getPrimaryHash(key);
        if (storage[primaryIndex] == null) {
            if (primaryIndex == 0) {
                storage[primaryIndex] = new boolean[secondaryBuckets + 1];
            } else {
                storage[primaryIndex] = new boolean[secondaryBuckets];
            }
        }
        int secondaryIndex = getSecondaryHash(key);
        storage[primaryIndex][secondaryIndex] = true;
    }

    // remove and contains methods similarly adjusted
}

Hi,

I see this as a secondary/alternative approach if we do not want to explicitly check 0th index condition and overflow. We initialized the primary bucket with size as 1001 to handle that division scenario. This approach was also suggested by the instrustor in the class and got accepted in leetcode. Could you please explain if I am missing anything.

[super30admin]

Strengths:

• The code is well-commented and the student has explained their approach.
• For the MinStack problem, the solution is correct and efficient.

Areas for Improvement:

• For the HashSet problem, the primary hash function should use modulo operation instead of division. The reference solution uses key % primaryBuckets for the primary hash and key / secondaryBuckets for the secondary hash. This ensures that the keys are properly distributed.
• You need to handle the edge case for key=1000000. In the reference solution, the first bucket (index 0) is allocated an array of size 1001 instead of 1000 to avoid index out of bounds for key=1000000.
• The primaryBuckets and secondaryBuckets values should be chosen such that the maximum key (10^6) is covered. The reference solution uses 1000 for both, but with a special case for the first bucket.
• In the HashSet solution, the primaryBuckets is set to 1001 in your code, which is acceptable, but the hashing functions need to be adjusted.

Suggested correction for HashSet:

class MyHashSet {
    boolean[][] arr;
    int primaryBuckets;
    int secondaryBuckets;

    public MyHashSet() {
        this.primaryBuckets = 1000;
        this.secondaryBuckets = 1000;
        this.arr = new boolean[primaryBuckets][];
    }

    private int getPrimaryHash(int key) {
        return key % primaryBuckets;
    }

    private int getSecondaryHash(int key) {
        return key / secondaryBuckets;
    }

    public void add(int key) {
        int primaryHash = getPrimaryHash(key);
        if(arr[primaryHash] == null) {
            // For the first bucket (index 0), we need to accommodate key=1000000 which has secondary index 1000
            if(primaryHash == 0) {
                arr[primaryHash] = new boolean[secondaryBuckets + 1];
            } else {
                arr[primaryHash] = new boolean[secondaryBuckets];
            }
        }
        int secondaryHash = getSecondaryHash(key);
        arr[primaryHash][secondaryHash] = true;
    }

    // remove and contains methods similarly adjusted
}