算法面试通关40讲 - 哈希表/映射

1. 两数之和

#include <iostream>
#include <unordered_map>
using namespace std;
class Solution {
public:
  vector<int> twoSum(vector<int> &nums, int target) {
    vector<int> indices;
    unordered_map<int, decltype(nums.size())> left; // val -> index
    for (decltype(nums.size()) i = 0; i < nums.size(); ++i) {
      auto itr = left.find(target - nums[i]);
      if (itr == left.end()) {
        left[nums[i]] = i;
      } else {
        indices.push_back(itr->second);
        indices.push_back(i);
        break;
      }
    }
    return indices;
  }
};