57 lines
1.6 KiB
Dart
57 lines
1.6 KiB
Dart
/**
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* File: subset_sum_i.dart
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* Created Time: 2023-08-10
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* Author: liuyuxin (gvenusleo@gmail.com)
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*/
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/* Backtracking algorithm: Subset Sum I */
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void backtrack(
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List<int> state,
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int target,
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List<int> choices,
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int start,
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List<List<int>> res,
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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(List.from(state));
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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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for (int i = start; i < choices.length; i++) {
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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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// 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, res);
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// Retract: undo the choice, restore to the previous state
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state.removeLast();
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}
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}
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/* Solve Subset Sum I */
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List<List<int>> subsetSumI(List<int> nums, int target) {
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List<int> state = []; // State (subset)
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nums.sort(); // Sort nums
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int start = 0; // Start point for traversal
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List<List<int>> res = []; // 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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void main() {
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List<int> nums = [3, 4, 5];
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int target = 9;
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List<List<int>> res = subsetSumI(nums, target);
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print("Input array nums = $nums, target = $target");
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print("All subsets equal to $target res = $res");
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}
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