677. Map Sum Pairs

Design a map that allows you to do the following:

• Maps a string key to a given value.
• Returns the sum of the values that have a key with a prefix equal to a given string.

Implement the MapSum class:

• MapSum() Initializes the MapSum object.
• void insert(String key, int val) Inserts the key-val pair into the map. If the key already existed, the original key-value pair will be overridden to the new one.
• int sum(string prefix) Returns the sum of all the pairs’ value whose key starts with the prefix.
   

Example 1:

Input:
[“MapSum”, “insert”, “sum”, “insert”, “sum”]
[[], [“apple”, 3], [“ap”], [“app”, 2], [“ap”]]
Output:
[null, null, 3, null, 5]
Explanation:
MapSum mapSum = new MapSum();
mapSum.insert(“apple”, 3);
mapSum.sum(“ap”); // return 3 (apple = 3)
mapSum.insert(“app”, 2);
mapSum.sum(“ap”); // return 5 (apple + app = 3 + 2 = 5)

Constraints:

• 1 <= key.length, prefix.length <= 50
• key and prefix consist of only lowercase English letters.
• 1 <= val <= 1000
• At most 50 calls will be made to insert and sum.

From: LeetCode
Link: 677. Map Sum Pairs

Solution:

Ideas:

• Trie Node value holds the sum of values of all keys passing through that node.

• A separate hashmap is used to track the current value of keys and to calculate the delta when updating an existing key.

• The sum operation just walks down the Trie using the prefix and returns the stored value.

Code:

#define ALPHABET_SIZE 26
#define MAX_KEY_LEN 51
#define HASH_MAP_SIZE 1000

typedef struct TrieNode {
    int value;
    struct TrieNode* children[ALPHABET_SIZE];
} TrieNode;

typedef struct KeyValue {
    char key[MAX_KEY_LEN];
    int val;
    struct KeyValue* next;
} KeyValue;

typedef struct {
    TrieNode* root;
    KeyValue* hashMap[HASH_MAP_SIZE];
} MapSum;

// Hash function for key
unsigned int hash(char* key) {
    unsigned int hash = 5381;
    while (*key)
        hash = ((hash << 5) + hash) + *key++;
    return hash % HASH_MAP_SIZE;
}

KeyValue* findKeyValue(KeyValue* head, const char* key) {
    while (head) {
        if (strcmp(head->key, key) == 0)
            return head;
        head = head->next;
    }
    return NULL;
}

TrieNode* createTrieNode() {
    TrieNode* node = (TrieNode*)calloc(1, sizeof(TrieNode));
    return node;
}

MapSum* mapSumCreate() {
    MapSum* obj = (MapSum*)malloc(sizeof(MapSum));
    obj->root = createTrieNode();
    for (int i = 0; i < HASH_MAP_SIZE; ++i)
        obj->hashMap[i] = NULL;
    return obj;
}

void insertToTrie(TrieNode* root, const char* key, int delta) {
    TrieNode* node = root;
    while (*key) {
        int index = *key - 'a';
        if (!node->children[index])
            node->children[index] = createTrieNode();
        node = node->children[index];
        node->value += delta;
        key++;
    }
}

void mapSumInsert(MapSum* obj, char* key, int val) {
    unsigned int h = hash(key);
    KeyValue* entry = findKeyValue(obj->hashMap[h], key);
    int oldVal = 0;

    if (entry) {
        oldVal = entry->val;
        entry->val = val;
    } else {
        entry = (KeyValue*)malloc(sizeof(KeyValue));
        strcpy(entry->key, key);
        entry->val = val;
        entry->next = obj->hashMap[h];
        obj->hashMap[h] = entry;
    }

    insertToTrie(obj->root, key, val - oldVal);
}

int mapSumSum(MapSum* obj, char* prefix) {
    TrieNode* node = obj->root;
    while (*prefix) {
        int index = *prefix - 'a';
        if (!node->children[index])
            return 0;
        node = node->children[index];
        prefix++;
    }
    return node->value;
}

void freeTrie(TrieNode* node) {
    if (!node) return;
    for (int i = 0; i < ALPHABET_SIZE; ++i)
        freeTrie(node->children[i]);
    free(node);
}

void freeHashMap(KeyValue* head) {
    while (head) {
        KeyValue* temp = head;
        head = head->next;
        free(temp);
    }
}

void mapSumFree(MapSum* obj) {
    freeTrie(obj->root);
    for (int i = 0; i < HASH_MAP_SIZE; ++i)
        freeHashMap(obj->hashMap[i]);
    free(obj);
}