Leetcode 220. Contains Duplicate III (Sliding window + set)

1. Contains Duplicate III
   Hard
   You are given an integer array nums and two integers indexDiff and valueDiff.

Find a pair of indices (i, j) such that:

i != j,
abs(i - j) <= indexDiff.
abs(nums[i] - nums[j]) <= valueDiff, and
Return true if such pair exists or false otherwise.

Example 1:

Input: nums = [1,2,3,1], indexDiff = 3, valueDiff = 0
Output: true
Explanation: We can choose (i, j) = (0, 3).
We satisfy the three conditions:
i != j --> 0 != 3
abs(i - j) <= indexDiff --> abs(0 - 3) <= 3
abs(nums[i] - nums[j]) <= valueDiff --> abs(1 - 1) <= 0
Example 2:

Input: nums = [1,5,9,1,5,9], indexDiff = 2, valueDiff = 3
Output: false
Explanation: After trying all the possible pairs (i, j), we cannot satisfy the three conditions, so we return false.

Constraints:

2 <= nums.length <= 105
-109 <= nums[i] <= 109
1 <= indexDiff <= nums.length
0 <= valueDiff <= 109

解法1：这题要用到set的lower_bound函数，表示在set里面最小的那个>=输入值的那个元素。

class Solution {
public:
    bool containsNearbyAlmostDuplicate(vector<int>& nums, int indexDiff, int valueDiff) {
        int n = nums.size();
        int left = 0, right = 0;
    //    unordered_map<int, int> mp; //<value, index>  注意用map不对，因为要检测map里面所有的entry，时间复杂度高。
        set<int> s;
        while (right < n) {
            //mp[nums[right]] = right;
            auto iter = s.lower_bound(nums[right]);
            if (iter != s.end()) {
                if (*iter - nums[right] <= valueDiff) return true;
            }
            iter = s.lower_bound(nums[right]);                
            if (iter != s.begin()) {
                iter--;
                if (nums[right] - *iter <= valueDiff) return true;
            }
            
            s.insert(nums[right]);
            right++;
            while (right - left > indexDiff) {
                s.erase(nums[left]);
                left++;
            }
        }
        return false;
    }
};