53 lines
1.5 KiB
C#
53 lines
1.5 KiB
C#
/**
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* File: two_sum.cs
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* Created Time: 2022-12-23
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* Author: haptear (haptear@hotmail.com)
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*/
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namespace hello_algo.chapter_searching;
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public class two_sum {
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/* Method one: Brute force enumeration */
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int[] TwoSumBruteForce(int[] nums, int target) {
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int size = nums.Length;
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// Two-layer loop, time complexity is O(n^2)
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for (int i = 0; i < size - 1; i++) {
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for (int j = i + 1; j < size; j++) {
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if (nums[i] + nums[j] == target)
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return [i, j];
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}
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}
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return [];
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}
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/* Method two: Auxiliary hash table */
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int[] TwoSumHashTable(int[] nums, int target) {
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int size = nums.Length;
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// Auxiliary hash table, space complexity is O(n)
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Dictionary<int, int> dic = [];
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// Single-layer loop, time complexity is O(n)
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for (int 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.Add(nums[i], i);
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}
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return [];
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}
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[Test]
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public void Test() {
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// ======= Test Case =======
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int[] nums = [2, 7, 11, 15];
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int target = 13;
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// ====== Driver Code ======
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// Method one
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int[] res = TwoSumBruteForce(nums, target);
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Console.WriteLine("Method one result = " + string.Join(", ", res));
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// Method two
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res = TwoSumHashTable(nums, target);
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Console.WriteLine("Method two result = " + string.Join(", ", res));
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}
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}
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