LeetCode in Kotlin

241. Different Ways to Add Parentheses

Medium

Given a string expression of numbers and operators, return all possible results from computing all the different possible ways to group numbers and operators. You may return the answer in any order.

Example 1:

Input: expression = “2-1-1”

Output: [0,2]

Explanation: ((2-1)-1) = 0 (2-(1-1)) = 2

Example 2:

Input: expression = “2*3-4*5”

Output: [-34,-14,-10,-10,10]

Explanation:

(2*(3-(4*5))) = -34
((2*3)-(4*5)) = -14
((2*(3-4))*5) = -10
(2*((3-4)*5)) = -10
(((2*3)-4)*5) = 10 

Constraints:

• 1 <= expression.length <= 20
• expression consists of digits and the operator '+', '-', and '*'.
• All the integer values in the input expression are in the range [0, 99].

Solution

class Solution {
    fun diffWaysToCompute(expression: String): List<Int> {
        return diffWayToCompute(expression, hashMapOf())
    }

    private fun diffWayToCompute(expression: String, hashMap: HashMap<String, List<Int>>): List<Int> {
        if (hashMap.containsKey(expression)) {
            return hashMap.getValue(expression)
        }
        val newList = arrayListOf<Int>()
        if (!hasOperatorInBetween(expression)) {
            newList.add(Integer.parseInt(expression))
        } else {
            for ((index, _) in expression.withIndex()) {
                val operator = expression[index]
                if (!Character.isDigit(operator)) {
                    val leftExpression = diffWayToCompute(expression.substring(0, index), hashMap)
                    val rightExpression = diffWayToCompute(expression.substring(index + 1), hashMap)
                    for (l in leftExpression) {
                        for (r in rightExpression) {
                            when (operator) {
                                '+' -> newList.add(l + r)
                                '-' -> newList.add(l - r)
                                '*' -> newList.add(l * r)
                            }
                        }
                    }
                }
            }
        }
        hashMap[expression] = newList
        return newList
    }

    private fun hasOperatorInBetween(expression: String): Boolean {
        for ((index, _) in expression.withIndex()) {
            when (expression[index]) {
                '+' -> return true
                '-' -> return true
                '*' -> return true
            }
        }
        return false
    }
}

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