62 lines
2.1 KiB
Kotlin
62 lines
2.1 KiB
Kotlin
/**
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* File: subset_sum_ii.kt
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* Created Time: 2024-01-25
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* Author: curtishd (1023632660@qq.com)
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*/
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package chapter_backtracking.subset_sum_ii
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/* Backtracking algorithm: Subset Sum II */
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fun backtrack(
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state: MutableList<Int>,
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target: Int,
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choices: IntArray,
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start: Int,
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res: MutableList<MutableList<Int>?>
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) {
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// When the subset sum equals target, record the solution
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if (target == 0) {
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res.add(state.toMutableList())
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return
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}
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// Traverse all choices
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// Pruning two: start traversing from start to avoid generating duplicate subsets
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// Pruning three: start traversing from start to avoid repeatedly selecting the same element
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for (i in start..<choices.size) {
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// Pruning one: if the subset sum exceeds target, end the loop immediately
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// This is because the array is sorted, and later elements are larger, so the subset sum will definitely exceed target
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if (target - choices[i] < 0) {
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break
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}
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// Pruning four: if the element equals the left element, it indicates that the search branch is repeated, skip it
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if (i > start && choices[i] == choices[i - 1]) {
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continue
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}
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// Attempt: make a choice, update target, start
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state.add(choices[i])
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// Proceed to the next round of selection
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backtrack(state, target - choices[i], choices, i + 1, res)
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// Retract: undo the choice, restore to the previous state
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state.removeAt(state.size - 1)
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}
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}
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/* Solve Subset Sum II */
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fun subsetSumII(nums: IntArray, target: Int): MutableList<MutableList<Int>?> {
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val state = mutableListOf<Int>() // State (subset)
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nums.sort() // Sort nums
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val start = 0 // Start point for traversal
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val res = mutableListOf<MutableList<Int>?>() // Result list (subset list)
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backtrack(state, target, nums, start, res)
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return res
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}
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/* Driver Code */
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fun main() {
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val nums = intArrayOf(4, 4, 5)
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val target = 9
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val res = subsetSumII(nums, target)
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println("Input array nums = ${nums.contentToString()}, target = $target")
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println("All subsets equal to $target res = $res")
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} |