mirror of
https://github.com/krahets/hello-algo.git
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e720aa2d24
* Sync recent changes to the revised Word. * Revised the preface chapter * Revised the introduction chapter * Revised the computation complexity chapter * Revised the chapter data structure * Revised the chapter array and linked list * Revised the chapter stack and queue * Revised the chapter hashing * Revised the chapter tree * Revised the chapter heap * Revised the chapter graph * Revised the chapter searching * Reivised the sorting chapter * Revised the divide and conquer chapter * Revised the chapter backtacking * Revised the DP chapter * Revised the greedy chapter * Revised the appendix chapter * Revised the preface chapter doubly * Revised the figures
53 lines
1.6 KiB
Java
53 lines
1.6 KiB
Java
/**
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* File: two_sum.java
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* Created Time: 2022-11-25
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* Author: Krahets (krahets@163.com)
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*/
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package chapter_searching;
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import java.util.*;
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public class two_sum {
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/* 方法一：暴力枚举 */
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static int[] twoSumBruteForce(int[] nums, int target) {
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int size = nums.length;
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// 两层循环，时间复杂度为 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 new int[] { i, j };
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}
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}
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return new int[0];
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}
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/* 方法二：辅助哈希表 */
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static int[] twoSumHashTable(int[] nums, int target) {
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int size = nums.length;
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// 辅助哈希表，空间复杂度为 O(n)
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Map<Integer, Integer> dic = new HashMap<>();
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// 单层循环，时间复杂度为 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 new int[] { dic.get(target - nums[i]), i };
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}
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dic.put(nums[i], i);
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}
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return new int[0];
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}
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public static void main(String[] args) {
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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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// 方法一
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int[] res = twoSumBruteForce(nums, target);
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System.out.println("方法一 res = " + Arrays.toString(res));
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// 方法二
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res = twoSumHashTable(nums, target);
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System.out.println("方法二 res = " + Arrays.toString(res));
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}
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}
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