leetcode刷题，总结，记录，备忘 287

leetcode287Find the Duplicate Number

Given an array nums containing n + 1 integers where each integer is between 1 and n (inclusive), prove that at least one duplicate number must exist. Assume that there is only one duplicate number, find the duplicate one.

Note:

1. You must not modify the array (assume the array is read only).
2. You must use only constant, O(1) extra space.
3. Your runtime complexity should be less than O(n2).
4. There is only one duplicate number in the array, but it could be repeated more than once.

熟练使用stl容器可大大降低该题目难度。用set容器，遍历数组，往set里insert，失败的时候即返回。

class Solution {public:    int findDuplicate(vector<int>& nums) {        set<int> si;                for (vector<int>::iterator it = nums.begin(); it != nums.end(); ++it)        {            pair<set<int>::iterator, bool> p = si.insert(*it);            if (p.second)            {                continue;            }            else            {                return *it;            }        }    }};