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50 lines
1.2 KiB
50 lines
1.2 KiB
7 months ago
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/**
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* File: two_sum.dart
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* Created Time: 2023-2-11
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* Author: Jefferson (JeffersonHuang77@gmail.com)
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*/
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import 'dart:collection';
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/* 方法一： 暴力列舉 */
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List<int> twoSumBruteForce(List<int> nums, int target) {
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int size = nums.length;
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// 兩層迴圈，時間複雜度為 O(n^2)
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for (var i = 0; i < size - 1; i++) {
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for (var j = i + 1; j < size; j++) {
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if (nums[i] + nums[j] == target) return [i, j];
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}
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}
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return [0];
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}
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/* 方法二： 輔助雜湊表 */
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List<int> twoSumHashTable(List<int> nums, int target) {
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int size = nums.length;
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// 輔助雜湊表，空間複雜度為 O(n)
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Map<int, int> dic = HashMap();
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// 單層迴圈，時間複雜度為 O(n)
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for (var i = 0; i < size; i++) {
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if (dic.containsKey(target - nums[i])) {
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return [dic[target - nums[i]]!, i];
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}
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dic.putIfAbsent(nums[i], () => i);
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}
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return [0];
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}
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/* Driver Code */
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void main() {
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// ======= Test Case =======
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List<int> nums = [2, 7, 11, 15];
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int target = 13;
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// ====== Driver Code ======
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// 方法一
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List<int> res = twoSumBruteForce(nums, target);
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print('方法一 res = $res');
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// 方法二
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res = twoSumHashTable(nums, target);
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print('方法二 res = $res');
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}
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