[LeetCode] Find All Duplicates in an Array

https://leetcode.com/problems/find-all-duplicates-in-an-array/#/description

像这种数组元素大小能够被bound且和数组size扯上关系，要条件反射想到类似bucket的做法。

类似的题：
leetcode 41 first missing positive
leetcode 287 find the duplicate number

class Solution {
public:
    vector<int> findDuplicates(vector<int>& nums) {
        if (nums.empty()) {
            return vector<int>();
        }
        vector<int> ret;
        for (int i = 0; i < nums.size(); ++i) {
            int true_pos = nums[i] - 1;
            if (nums[i] != i+1 && nums[i] != 0) {
                if (nums[i] == nums[true_pos]) {
                    ret.push_back(nums[i]);
                    nums[i] = 0;
                } else {
                    std::swap(nums[i], nums[true_pos]);
                    i--;
                }
            }
        }
        return ret;
    }
};