Contains Duplicate II

Description

Given an integer array nums and an integer k, return true if there are two distinct indices i and j in the array such that nums[i] == nums[j] and abs(i - j) <= k.

Example 1:

Input: nums = [1,2,3,1], k = 3 Output: true

Example 2:

Input: nums = [1,0,1,1], k = 1 Output: true

Example 3:

Input: nums = [1,2,3,1,2,3], k = 2 Output: false

Constraints:

• 1 <= nums.length <= 105
• -109 <= nums[i] <= 109
• 0 <= k <= 105

Code

關於 m[nums[i]] = i;：

我們可以一直更新 m 中的 nums[i] 對應的 index，因為如果叫靠後的 index 也無法滿足條件 abs(i - j) <= k，更之前的就更沒辦法，所以可以直接用後面的 index 取代前面的。

class Solution {
public:
    bool containsNearbyDuplicate(vector<int>& nums, int k) {
        unordered_map<int, int> m;
        for(int i = 0; i < nums.size(); i++) {
            if(m.find(nums[i]) != m.end()) {
                int j = m[nums[i]];
                if(abs(i - j) <= k) return true;
            } 
            m[nums[i]] = i;
        }
 
        return false;
    }
};

Source

• Contains Duplicate II - LeetCode