LeetCode in Kotlin

40. Combination Sum II

Medium

Given a collection of candidate numbers (candidates) and a target number (target), find all unique combinations in candidates where the candidate numbers sum to target.

Each number in candidates may only be used once in the combination.

Note: The solution set must not contain duplicate combinations.

Example 1:

Input: candidates = [10,1,2,7,6,1,5], target = 8

Output: [ [1,1,6], [1,2,5], [1,7], [2,6] ]

Example 2:

Input: candidates = [2,5,2,1,2], target = 5

Output: [ [1,2,2], [5] ]

Constraints:

• 1 <= candidates.length <= 100
• 1 <= candidates[i] <= 50
• 1 <= target <= 30

Solution

import java.util.LinkedList

class Solution {
    fun combinationSum2(candidates: IntArray, target: Int): List<List<Int>> {
        val sums: MutableList<List<Int>> = ArrayList()
        // optimize
        candidates.sort()
        combinationSum(candidates, target, 0, sums, LinkedList())
        return sums
    }

    private fun combinationSum(
        candidates: IntArray,
        target: Int,
        start: Int,
        sums: MutableList<List<Int>>,
        sum: LinkedList<Int>
    ) {
        if (target == 0) {
            // make a deep copy of the current combination
            sums.add(ArrayList(sum))
            return
        }
        var i = start
        while (i < candidates.size && target >= candidates[i]) {

            // If candidate[i] equals candidate[i-1], then solutions for i is subset of
            // solution of i-1
            if (i == start || i > start && candidates[i] != candidates[i - 1]) {
                sum.addLast(candidates[i])
                // call on 'i+1' (not i) to avoid duplicate usage of same element
                combinationSum(candidates, target - candidates[i], i + 1, sums, sum)
                sum.removeLast()
            }
            i++
        }
    }
}

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