Merge pull request #957 from 0xff-dev/719

Add solution and test-cases for problem 719

leetcode/701-800/0719.Find-K-th-Smallest-Pair-Distance/README.md

@@ -1,28 +1,35 @@
 # [719.Find K-th Smallest Pair Distance][title]
 
-> [!WARNING|style:flat]
-> This question is temporarily unanswered if you have good ideas. Welcome to [Create Pull Request PR](https://github.com/kylesliu/awesome-golang-algorithm)
-
 ## Description
+The **distance of a pair** of integers `a` and `b` is defined as the absolute difference between `a` and `b`.
+
+Given an integer array `nums` and an integer `k`, return the `kth` smallest **distance among all the pairs** `nums[i]` and `nums[j]` where `0 <= i < j < nums.length`.
 
 **Example 1:**
 
 ```
-Input: a = "11", b = "1"
-Output: "100"
+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.
 ```
 
-## 题意
-> ...
+**Example 2:**
 
-## 题解
-
-### 思路1
-> ...
-Find K-th Smallest Pair Distance
-```go
+```
+Input: nums = [1,1,1], k = 2
+Output: 0
 ```
 
+**Example 3:**
+
+```
+Input: nums = [1,6,1], k = 3
+Output: 5
+```
 
 ## 结语
 

leetcode/701-800/0719.Find-K-th-Smallest-Pair-Distance/Solution.go

@@ -1,5 +1,41 @@
 package Solution
 
-func Solution(x bool) bool {
-	return x
+import "sort"
+
+func Solution(nums []int, k int) int {
+	sort.Ints(nums)
+	// 通常情况下 那基本就是n^2 + nlog(n)了，计算出全部，然后重新排列
+	// 对于条件i < j, 就是选择(i, j)或者(j, i)的问题, 可以直接忽略了
+	// 如果完全计算，肯定是不行的，10^8 如果选择最后几个元素，内存都要爆炸
+	l := len(nums)
+	var count func(int) int
+	count = func(target int) int {
+		ans := 0
+		// 4, 62, 100
+		for i := 1; i < l; i++ {
+			idx := sort.Search(i, func(ii int) bool {
+				return nums[i]-nums[ii] <= target
+			})
+			ans += i - idx
+		}
+		return ans
+	}
+	a, b := 0, nums[l-1]-nums[0]
+	// 查看小于等于当前值的有多少个
+	// 4, 62, 100
+	// 38,58,96,
+	// 0, 5, 5
+	// 0 ~ 5
+	// 3 ~ 5
+	// 4 ~ 5
+	for a < b {
+		mid := (a + b) / 2
+		c := count(mid)
+		if c < k {
+			a = mid + 1
+			continue
+		}
+		b = mid
+	}
+	return a
 }

leetcode/701-800/0719.Find-K-th-Smallest-Pair-Distance/Solution_test.go

@@ -10,30 +10,31 @@ func TestSolution(t *testing.T) {
 	//	测试用例
 	cases := []struct {
 		name   string
-		inputs bool
-		expect bool
+		nums   []int
+		k      int
+		expect int
 	}{
-		{"TestCase", true, true},
-		{"TestCase", true, true},
-		{"TestCase", false, false},
+		{"TestCase1", []int{1, 3, 1}, 1, 0},
+		{"TestCase2", []int{1, 1, 1}, 2, 0},
+		{"TestCase3", []int{1, 6, 1}, 3, 5},
 	}
 
 	//	开始测试
 	for i, c := range cases {
 		t.Run(c.name+" "+strconv.Itoa(i), func(t *testing.T) {
-			got := Solution(c.inputs)
+			got := Solution(c.nums, c.k)
 			if !reflect.DeepEqual(got, c.expect) {
-				t.Fatalf("expected: %v, but got: %v, with inputs: %v",
-					c.expect, got, c.inputs)
+				t.Fatalf("expected: %v, but got: %v, with inputs: %v %v",
+					c.expect, got, c.nums, c.k)
 			}
 		})
 	}
 }
 
-//	压力测试
+// 压力测试
 func BenchmarkSolution(b *testing.B) {
 }
 
-//	使用案列
+// 使用案列
 func ExampleSolution() {
 }