问题
Input：numbers={2, 7, 11, 15}, target=9
Output: index1=1, index2=2
方案
用一个哈希表，存储每个数对应的下标，复杂度O(n)
代码
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| class Solution {
public:
vector<int> twoSum(vector<int> &nums, int target) {
unordered_map<int, int> mapping;
vector<int> result;
for (int i = 0; i < nums.size(); i++) {
mapping[nums[i]] = i;
}
for (int i = 0; i < nums.size(); i++) {
const int gap = target - nums[i];
if (mapping.find(gap) != mapping.end() && mapping[gap] > i) {
result.push_back(i + 1);
result.push_back(mapping[gap] + 1);
break;
}
}
return result;
}
};
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