LeetCode in Kotlin

677. Map Sum Pairs

Medium

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.

Solution

class MapSum {
    internal class Node {
        var `val`: Int = 0
        var child: Array<Node?> = arrayOfNulls(26)
    }

    private val root: Node = Node()

    fun insert(key: String, `val`: Int) {
        var curr: Node? = root
        for (c in key.toCharArray()) {
            if (curr!!.child[c.code - 'a'.code] == null) {
                curr.child[c.code - 'a'.code] = Node()
            }
            curr = curr.child[c.code - 'a'.code]
        }
        curr!!.`val` = `val`
    }

    private fun sumHelper(root: Node?): Int {
        var o = 0
        for (i in 0..25) {
            if (root!!.child[i] != null) {
                o += root.child[i]!!.`val` + sumHelper(root.child[i])
            }
        }
        return o
    }

    fun sum(prefix: String): Int {
        var curr: Node? = root
        for (c in prefix.toCharArray()) {
            if (curr!!.child[c.code - 'a'.code] == null) {
                return 0
            }
            curr = curr.child[c.code - 'a'.code]
        }
        val sum = curr!!.`val`
        return sum + sumHelper(curr)
    }
}

/*
 * Your MapSum object will be instantiated and called as such:
 * var obj = MapSum()
 * obj.insert(key,`val`)
 * var param_2 = obj.sum(prefix)
 */

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