mirror of
https://github.com/krahets/hello-algo.git
synced 2024-12-27 00:06:28 +08:00
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
54 lines
1.3 KiB
C++
54 lines
1.3 KiB
C++
/**
|
|
* File: two_sum.cpp
|
|
* Created Time: 2022-11-25
|
|
* Author: Krahets (krahets@163.com)
|
|
*/
|
|
|
|
#include "../utils/common.hpp"
|
|
|
|
/* 方法一：暴力枚举 */
|
|
vector<int> twoSumBruteForce(vector<int> &nums, int target) {
|
|
int size = nums.size();
|
|
// 两层循环，时间复杂度为 O(n^2)
|
|
for (int i = 0; i < size - 1; i++) {
|
|
for (int j = i + 1; j < size; j++) {
|
|
if (nums[i] + nums[j] == target)
|
|
return {i, j};
|
|
}
|
|
}
|
|
return {};
|
|
}
|
|
|
|
/* 方法二：辅助哈希表 */
|
|
vector<int> twoSumHashTable(vector<int> &nums, int target) {
|
|
int size = nums.size();
|
|
// 辅助哈希表，空间复杂度为 O(n)
|
|
unordered_map<int, int> dic;
|
|
// 单层循环，时间复杂度为 O(n)
|
|
for (int i = 0; i < size; i++) {
|
|
if (dic.find(target - nums[i]) != dic.end()) {
|
|
return {dic[target - nums[i]], i};
|
|
}
|
|
dic.emplace(nums[i], i);
|
|
}
|
|
return {};
|
|
}
|
|
|
|
/* Driver Code */
|
|
int main() {
|
|
// ======= Test Case =======
|
|
vector<int> nums = {2, 7, 11, 15};
|
|
int target = 13;
|
|
|
|
// ====== Driver Code ======
|
|
// 方法一
|
|
vector<int> res = twoSumBruteForce(nums, target);
|
|
cout << "方法一 res = ";
|
|
printVector(res);
|
|
// 方法二
|
|
res = twoSumHashTable(nums, target);
|
|
cout << "方法二 res = ";
|
|
printVector(res);
|
|
|
|
return 0;
|
|
}
|