55 lines
1.3 KiB
C++
55 lines
1.3 KiB
C++
/**
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* File: two_sum.cpp
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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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#include "../utils/common.hpp"
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/* 方法一：暴力枚举 */
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vector<int> twoSumBruteForce(vector<int> &nums, int target) {
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int size = nums.size();
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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 {i, j};
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}
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}
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return {};
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}
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/* 方法二：辅助哈希表 */
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vector<int> twoSumHashTable(vector<int> &nums, int target) {
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int size = nums.size();
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// 辅助哈希表，空间复杂度为 O(n)
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unordered_map<int, int> dic;
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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.find(target - nums[i]) != dic.end()) {
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return {dic[target - nums[i]], i};
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}
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dic.emplace(nums[i], i);
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}
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return {};
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}
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/* Driver Code */
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int main() {
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// ======= Test Case =======
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vector<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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vector<int> res = twoSumBruteForce(nums, target);
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cout << "方法一 res = ";
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printVector(res);
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// 方法二
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res = twoSumHashTable(nums, target);
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cout << "方法二 res = ";
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printVector(res);
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return 0;
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}
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