[LeetCode] 532. K-diff Pairs in an Array
grandyang opened this issue · comments
Given an array of integers and an integer k, you need to find the number of unique k-diff pairs in the array. Here a k-diff pair is defined as an integer pair (i, j), where i and j are both numbers in the array and their absolute difference is k.
Example 1:
Input: [3, 1, 4, 1, 5], k = 2
Output: 2
Explanation: There are two 2-diff pairs in the array, (1, 3) and (3, 5).
Although we have two 1s in the input, we should only return the number of unique pairs.
Example 2:
Input:[1, 2, 3, 4, 5], k = 1
Output: 4
Explanation: There are four 1-diff pairs in the array, (1, 2), (2, 3), (3, 4) and (4, 5).
Example 3:
Input: [1, 3, 1, 5, 4], k = 0
Output: 1
Explanation: There is one 0-diff pair in the array, (1, 1).
Note:
- The pairs (i, j) and (j, i) count as the same pair.
- The length of the array won't exceed 10,000.
- All the integers in the given input belong to the range: [-1e7, 1e7].
这道题给了我们一个含有重复数字的无序数组,还有一个整数k,让找出有多少对不重复的数对 (i, j) 使得i和j的差刚好为k。由于k有可能为0,而只有含有至少两个相同的数字才能形成数对,那么就是说需要统计数组中每个数字的个数。可以建立每个数字和其出现次数之间的映射,然后遍历 HashMap 中的数字,如果k为0且该数字出现的次数大于1,则结果 res 自增1;如果k不为0,且用当前数字加上k后得到的新数字也在数组中存在,则结果 res 自增1,参见代码如下:
解法一:
class Solution {
public:
int findPairs(vector<int>& nums, int k) {
int res = 0, n = nums.size();
unordered_map<int, int> m;
for (int num : nums) ++m[num];
for (auto a : m) {
if (k == 0 && a.second > 1) ++res;
if (k > 0 && m.count(a.first + k)) ++res;
}
return res;
}
};
下面这种方法没有使用 HashMap,而是使用了双指针,需要给数组排序,节省了空间的同时牺牲了时间。遍历排序后的数组,然后在当前数字之前找最后一个和当前数之差大于k的数字,若这个数字和当前数字不是同一个位置,且和上一轮 pre 不是同一个数字,且和当前数字之差正好为k,那么结果 res 自增1,然后将 pre 赋值为这个数字,参见代码如下:
解法二:
class Solution {
public:
int findPairs(vector<int>& nums, int k) {
int res = 0, n = nums.size(), j = 0, pre = INT_MAX;
sort(nums.begin(), nums.end());
for (int i = 1; i < n; ++i){
while (j < i && nums[i] - nums[j] > k) ++j;
if (j != i && pre != nums[j] && nums[i] - nums[j] == k) {
++res;
pre = nums[j];
}
}
return res;
}
};
Github 同步地址:
类似题目:
Minimum Absolute Difference in BST
参考资料:
https://leetcode.com/problems/k-diff-pairs-in-an-array/submissions/
https://leetcode.com/problems/k-diff-pairs-in-an-array/discuss/100104/two-pointer-approach