Leetcode: Map Sum Pairs

Map Sum Pairs



Similar Problems:


Implement a MapSum class with insert, and sum methods.

For the method insert, you’ll be given a pair of (string, integer). The string represents the key and the integer represents the value. If the key already existed, then the original key-value pair will be overridden to the new one.

For the method sum, you’ll be given a string representing the prefix, and you need to return the sum of all the pairs’ value whose key starts with the prefix.

Example 1:

Input: insert("apple", 3), Output: Null
Input: sum("ap"), Output: 3
Input: insert("app", 2), Output: Null
Input: sum("ap"), Output: 5

Github: code.dennyzhang.com

Credits To: leetcode.com

Leave me comments, if you have better ways to solve.


// Blog link: https://code.dennyzhang.com/map-sum-pairs
// Basic Ideas: Trie Tree
// Complexity: Time ?, Space ?

type MapSum struct {
    children map[string]*MapSum
    val int
    isLeaf bool
}

/** Initialize your data structure here. */
func Constructor() MapSum {
    root := MapSum{make(map[string]*MapSum), 0, false}
    return root
}

func (this *MapSum) Insert(key string, val int)  {
    node := this
    for i := 0; i < len(key); i++ {
        ch := string(key[i])
        p, ok := node.children[ch]
        if ok == false {
            p = &MapSum{make(map[string]*MapSum), 0, false}
            node.children[ch] = p
        }
        node = p
    }
    node.isLeaf = true
    node.val = val
}

func (this *MapSum) Sum(prefix string) int {
    node := this
    // fmt.Print(node, "\n")
    i := 0;
    for ; i < len(prefix); i++ {
        ch := string(prefix[i])
        p, ok := node.children[ch]
        if ok == true {
            node = p
        } else {
            break
        }
    }

    if i != len(prefix) {
        // haven't found this prefix
        return 0
    } else {
        // sum all the leaf nodes
        res := 0
        queue := []*MapSum{node}
        for len(queue) != 0 {
            queue_count := len(queue)
            for i:=0; i<queue_count; i++ {
                node = queue[0]
                // collect result of leaf
                if node.isLeaf == true {
                    res += node.val
                }
                queue = queue[1:]
                // get the next level
                for ch := range node.children {
                    queue = append(queue, node.children[ch])
                }
            }
        }
        return res
    }
}

/**
 * Your MapSum object will be instantiated and called as such:
 * obj := Constructor();
 * obj.Insert(key,val);
 * param_2 := obj.Sum(prefix);
 */
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