219. Contains Duplicate II

Given an array of integers and an integer k, find out whether there are two distinct indices i and j

in the array such that nums[i] = nums[j] and the difference between i and j is at most k.

思路：

哈希表查找就好，将数组数值和下标挂钩，如果发现表中存在该数值，比较下标距离即可。注意，这题是证明是否存在这种组合，而不是所有重复数字都得满足，存在即可。

bool containsNearbyDuplicate(vector<int>& nums, int k) {
unordered_map<int, int> myhash;
for (int i = 0; i < nums.size(); i++) {
if (myhash.find(nums[i]) != myhash.end()) {
int j = myhash[nums[i]];
if (i - j <= k) return true;
else myhash[nums[i]] = i;
//这里更新下标很重要，因为对于后面可能出现的重复要保证求得目前的最近的下标，看有没有可能满足要求
}
else
myhash[nums[i]] = i;
}
return false;
}