Add solution 825

leetcode/0825.Friends-Of-Appropriate-Ages/825. Friends Of Appropriate Ages.go

@@ -0,0 +1,27 @@
+package leetcocde
+
+func numFriendRequests(ages []int) int {
+	res, count := 0, [125]int{}
+	for _, x := range ages {
+		count[x]++
+	}
+	for i := 1; i <= 120; i++ {
+		for j := 1; j <= 120; j++ {
+			if j > i {
+				continue
+			}
+			if (j-7)*2 <= i {
+				continue
+			}
+			if j > 100 && i < 100 {
+				continue
+			}
+			if i != j {
+				res += count[i] * count[j]
+			} else {
+				res += count[i] * (count[j] - 1)
+			}
+		}
+	}
+	return res
+}

leetcode/0825.Friends-Of-Appropriate-Ages/825. Friends Of Appropriate Ages_test.go

@@ -0,0 +1,52 @@
+package leetcocde
+
+import (
+	"fmt"
+	"testing"
+)
+
+type question825 struct {
+	para825
+	ans825
+}
+
+// para 是参数
+// one 代表第一个参数
+type para825 struct {
+	ages []int
+}
+
+// ans 是答案
+// one 代表第一个答案
+type ans825 struct {
+	one int
+}
+
+func Test_Problem825(t *testing.T) {
+
+	qs := []question825{
+
+		{
+			para825{[]int{16, 16}},
+			ans825{2},
+		},
+
+		{
+			para825{[]int{16, 17, 18}},
+			ans825{2},
+		},
+
+		{
+			para825{[]int{20, 30, 100, 110, 120}},
+			ans825{3},
+		},
+	}
+
+	fmt.Printf("------------------------Leetcode Problem 825------------------------\n")
+
+	for _, q := range qs {
+		_, p := q.ans825, q.para825
+		fmt.Printf("【input】:%v       【output】:%v\n", p, numFriendRequests(p.ages))
+	}
+	fmt.Printf("\n\n\n")
+}

leetcode/0825.Friends-Of-Appropriate-Ages/README.md

@@ -0,0 +1,99 @@
+# [825. Friends Of Appropriate Ages](https://leetcode.com/problems/friends-of-appropriate-ages/)
+
+
+## 题目
+
+There are `n` persons on a social media website. You are given an integer array `ages` where `ages[i]` is the age of the `ith` person.
+
+A Person `x` will not send a friend request to a person `y` (`x != y`) if any of the following conditions is true:
+
+- `age[y] <= 0.5 * age+ 7`
+- `age[y] > age[x]`
+- `age[y] > 100 && age< 100`
+
+Otherwise, `x` will send a friend request to `y`.
+
+Note that if `x` sends a request to `y`, `y` will not necessarily send a request to `x`. Also, a person will not send a friend request to themself.
+
+Return *the total number of friend requests made*.
+
+**Example 1:**
+
+```
+Input: ages = [16,16]
+Output: 2
+Explanation: 2 people friend request each other.
+
+```
+
+**Example 2:**
+
+```
+Input: ages = [16,17,18]
+Output: 2
+Explanation: Friend requests are made 17 -> 16, 18 -> 17.
+
+```
+
+**Example 3:**
+
+```
+Input: ages = [20,30,100,110,120]
+Output: 3
+Explanation: Friend requests are made 110 -> 100, 120 -> 110, 120 -> 100.
+
+```
+
+**Constraints:**
+
+- `n == ages.length`
+- `1 <= n <= 2 * 10^4`
+- `1 <= ages[i] <= 120`
+
+## 题目大意
+
+在社交媒体网站上有 n 个用户。给你一个整数数组 ages ，其中 ages[i] 是第 i 个用户的年龄。
+
+如果下述任意一个条件为真，那么用户 x 将不会向用户 y（x != y）发送好友请求：
+
+- ages[y] <= 0.5 * ages[x] + 7
+- ages[y] > ages[x]
+- ages[y] > 100 && ages[x] < 100
+
+否则，x 将会向 y 发送一条好友请求。注意，如果 x 向 y 发送一条好友请求，y 不必也向 x 发送一条好友请求。另外，用户不会向自己发送好友请求。返回在该社交媒体网站上产生的好友请求总数。
+
+## 解题思路
+
+- 简单题。先统计 [1,120] 范围内每个年龄的人数。然后利用题目中的三个判断条件，筛选符合条件的用户对。需要注意的是，相同年龄的人可以相互发送好友请求。不同年龄的人发送好友请求是单向的，即年龄老的向年龄轻的发送好友请求，年龄轻的不会对年龄老的发送好友请求。
+
+## 代码
+
+```go
+package leetcocde
+
+func numFriendRequests(ages []int) int {
+	res, count := 0, [125]int{}
+	for _, x := range ages {
+		count[x]++
+	}
+	for i := 1; i <= 120; i++ {
+		for j := 1; j <= 120; j++ {
+			if j > i {
+				continue
+			}
+			if (j-7)*2 <= i {
+				continue
+			}
+			if j > 100 && i < 100 {
+				continue
+			}
+			if i != j {
+				res += count[i] * count[j]
+			} else {
+				res += count[i] * (count[j] - 1)
+			}
+		}
+	}
+	return res
+}
+```