From 9c17cebab96acf7e11334402fed7af992913b314 Mon Sep 17 00:00:00 2001
From: gameloader <ggwqqo@163.com>
Date: Wed, 13 Mar 2024 15:28:11 +0800
Subject: [PATCH] leetcode update

---
 content/posts/leetcode.md | 49 +++++++++++++++++++++++++++++++++++++++
 1 file changed, 49 insertions(+)

diff --git a/content/posts/leetcode.md b/content/posts/leetcode.md
index f01f680..26aa282 100644
--- a/content/posts/leetcode.md
+++ b/content/posts/leetcode.md
@@ -993,3 +993,52 @@ func removeZeroSumSublists(head *ListNode) *ListNode {
 ### 总结
 
 删除中间部分节点的前缀和对应的key的项时, 考虑到中间部分的和一定为0, 因此用sum去累加中间部分节点的值并依次删除, 最后得到的sum就和删除节点开始前的sum相同. 本题一是要清楚通过前缀和来寻找连续的和为0的序列, 另一方面则是时刻记住这个序列的和为0的特性. 其实本题有一种代表元的抽象思想. 可以将一组和为0的序列看为一个, 其在加和过程中与不存在的节点具有等价性. 不影响和的变化.
+
+## day16 2024-03-13
+
+### 2485. Find the Pivot Integer
+
+Given a positive integer n, find the pivot integer x such that:
+
+The sum of all elements between 1 and x inclusively equals the sum of all elements between x and n inclusively.
+Return the pivot integer x. If no such integer exists, return -1. It is guaranteed that there will be at most one pivot index for the given input.
+
+Example 1:
+
+Input: n = 8
+Output: 6
+Explanation: 6 is the pivot integer since: 1 + 2 + 3 + 4 + 5 + 6 = 6 + 7 + 8 = 21.
+Example 2:
+
+Input: n = 1
+Output: 1
+Explanation: 1 is the pivot integer since: 1 = 1.
+Example 3:
+
+Input: n = 4
+Output: -1
+Explanation: It can be proved that no such integer exist.
+
+### 题解
+
+本题使用数学方法进行计算
+![0313p3Pvfwnneeh8](https://testingcf.jsdelivr.net/gh/game-loader/picbase@master/uPic/0313p3Pvfwnneeh8.png)
+根据公式直接求出x的值即可, 注意考虑到精度问题, 要对最终得到的运算结果与取整后的数字的差的绝对值进行判断, 小于一定限度即可认为是整数值.
+
+### 代码
+
+```go
+func pivotInteger(n int) int {
+    n_float := float64(n)
+    x := n_float*math.Sqrt(n_float+1)/math.Sqrt(2*n_float)
+    if math.Abs(x-float64(int(x))) < 0.0000001{
+        return int(x)
+    }else {
+        return -1
+    }
+}
+```
+
+### 总结
+
+查看他人解法发现本题其实也可以使用前缀和进行求解, 将每个下标位置处的前缀和求出并保存, 倒序遍历数组, 将后面的数的和与当前位置的前缀和比较即可, 示例代码