719. Find K-th Smallest Pair Distance

Given an integer array, return the k-th smallest distance among all the pairs. The distance of a pair (A, B) is defined as the absolute difference between A and B.

Example 1:

```Input:
nums = [1,3,1]
k = 1
Output: 0
Explanation:
Here are all the pairs:
(1,3) -> 2
(1,1) -> 0
(3,1) -> 2
Then the 1st smallest distance pair is (1,1), and its distance is 0.
```

Note:

1. `2 <= len(nums) <= 10000`.
2. `0 <= nums[i] < 1000000`.
3. `1 <= k <= len(nums) * (len(nums) - 1) / 2`.

719. Find K-th Smallest Pair Distance
``````struct Solution;

impl Solution {
fn smallest_distance_pair(mut nums: Vec<i32>, k: i32) -> i32 {
let n = nums.len();
nums.sort_unstable();
let mut lo = 0;
let mut hi = nums[n - 1] - nums[0];
while lo < hi {
let mi = lo + (hi - lo) / 2;
let mut count = 0;
let mut j = 1;
for i in 0..n - 1 {
while j < n && nums[j] - nums[i] <= mi {
j += 1;
}
count += j - 1 - i;
}
if count >= k as usize {
hi = mi;
} else {
lo = mi + 1;
}
}
lo
}
}

#[test]
fn test() {
let nums = vec![1, 3, 1];
let k = 1;
let res = 0;
assert_eq!(Solution::smallest_distance_pair(nums, k), res);
let nums = vec![62, 100, 4];
let k = 2;
let res = 58;
assert_eq!(Solution::smallest_distance_pair(nums, k), res);
}
``````