C++算法题_第一周

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Given an array of integers, 1 ≤ a[i] ≤ n (n = size of array), some elements appear twice and others appear once.

Find all the elements that appear twice in this array.

Could you do it without extra space and in O(n) runtime?

Example:

Input:[4,3,2,7,8,2,3,1]Output:[2,3]

题目解答

class Solution {public:    vector<int> findDuplicates(vector<int>& nums) {        int leng = nums.size();        map<int, bool> twice;        vector<int> ret;        for(int i = 0; i < leng; i++){        map<int, bool>::iterator it;        it = twice.find(nums[i]);        if(it != twice.end()) twice[nums[i]] = 1;        else{        twice[nums[i]] = 0;}}map<int, bool>::iterator itr;itr = twice.begin();for(; itr!=twice.end(); itr++){if((*itr).second) ret.push_back((*itr).first);}return ret;    }};