Update README

Author: halfrost

README.md

@@ -135,5 +135,5 @@ func romanToInt(s string) int {
 ----------------------------------------------
 <div style="display: flex;justify-content: space-between;align-items: center;">
 <p><a href="https://books.halfrost.com/leetcode/ChapterFour/0001~0099/0012.Integer-to-Roman/">⬅️上一页</a></p>
-<p><a href="https://books.halfrost.com/leetcode/ChapterFour/0001~0099/0015.3Sum/">下一页➡️</a></p>
+<p><a href="https://books.halfrost.com/leetcode/ChapterFour/0001~0099/0014.Longest-Common-Prefix/">下一页➡️</a></p>
 </div>

website/content/ChapterFour/0001~0099/0013.Roman-to-Integer.md

@@ -0,0 +1,71 @@
+# [14. Longest Common Prefix](https://leetcode.com/problems/longest-common-prefix/)
+
+## 题目
+
+Write a function to find the longest common prefix string amongst an array of strings.
+
+If there is no common prefix, return an empty string "".
+
+**Example 1**:
+
+    Input: strs = ["flower","flow","flight"]
+    Output: "fl"
+
+**Example 2**:
+
+    Input: strs = ["dog","racecar","car"]
+    Output: ""
+    Explanation: There is no common prefix among the input strings.
+
+**Constraints:**
+
+- 1 <= strs.length <= 200
+- 0 <= strs[i].length <= 200
+- strs[i] consists of only lower-case English letters.
+
+## 题目大意
+
+编写一个函数来查找字符串数组中的最长公共前缀。
+
+如果不存在公共前缀，返回空字符串 ""。
+
+## 解题思路
+
+- 对 strs 按照字符串长度进行升序排序，求出 strs 中长度最小字符串的长度 minLen
+- 逐个比较长度最小字符串与其它字符串中的字符，如果不相等就返回 commonPrefix,否则就把该字符加入 commonPrefix
+
+## 代码
+
+```go
+
+package leetcode
+
+import "sort"
+
+func longestCommonPrefix(strs []string) string {
+	sort.Slice(strs, func(i, j int) bool {
+		return len(strs[i]) <= len(strs[j])
+	})
+	minLen := len(strs[0])
+	if minLen == 0 {
+		return ""
+	}
+	var commonPrefix []byte
+	for i := 0; i < minLen; i++ {
+		for j := 1; j < len(strs); j++ {
+			if strs[j][i] != strs[0][i] {
+				return string(commonPrefix)
+			}
+		}
+		commonPrefix = append(commonPrefix, strs[0][i])
+	}
+	return string(commonPrefix)
+}
+```
+
+
+----------------------------------------------
+<div style="display: flex;justify-content: space-between;align-items: center;">
+<p><a href="https://books.halfrost.com/leetcode/ChapterFour/0001~0099/0013.Roman-to-Integer/">⬅️上一页</a></p>
+<p><a href="https://books.halfrost.com/leetcode/ChapterFour/0001~0099/0015.3Sum/">下一页➡️</a></p>
+</div>

website/content/ChapterFour/0001~0099/0014.Longest-Common-Prefix.md

@@ -120,6 +120,6 @@ func threeSum1(nums []int) [][]int {
 
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 <div style="display: flex;justify-content: space-between;align-items: center;">
-<p><a href="https://books.halfrost.com/leetcode/ChapterFour/0001~0099/0013.Roman-to-Integer/">⬅️上一页</a></p>
+<p><a href="https://books.halfrost.com/leetcode/ChapterFour/0001~0099/0014.Longest-Common-Prefix/">⬅️上一页</a></p>
 <p><a href="https://books.halfrost.com/leetcode/ChapterFour/0001~0099/0016.3Sum-Closest/">下一页➡️</a></p>
 </div>

website/content/ChapterFour/0001~0099/0015.3Sum.md

@@ -80,5 +80,5 @@ func maxProduct318(words []string) int {
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 <div style="display: flex;justify-content: space-between;align-items: center;">
 <p><a href="https://books.halfrost.com/leetcode/ChapterFour/0300~0399/0315.Count-of-Smaller-Numbers-After-Self/">⬅️上一页</a></p>
-<p><a href="https://books.halfrost.com/leetcode/ChapterFour/0300~0399/0322.Coin-Change/">下一页➡️</a></p>
+<p><a href="https://books.halfrost.com/leetcode/ChapterFour/0300~0399/0319.Bulb-Switcher/">下一页➡️</a></p>
 </div>

website/content/ChapterFour/0300~0399/0318.Maximum-Product-of-Word-Lengths.md

@@ -0,0 +1,65 @@
+# [319. Bulb Switcher](https://leetcode.com/problems/bulb-switcher/)
+
+
+## 题目
+
+There are n bulbs that are initially off. You first turn on all the bulbs, then you turn off every second bulb.
+
+On the third round, you toggle every third bulb (turning on if it's off or turning off if it's on). For the ith round, you toggle every i bulb. For the nth round, you only toggle the last bulb.
+
+Return the number of bulbs that are on after n rounds.
+
+**Example 1:**
+
+    Input: n = 3
+    Output: 1
+    Explanation: At first, the three bulbs are [off, off, off].
+    After the first round, the three bulbs are [on, on, on].
+    After the second round, the three bulbs are [on, off, on].
+    After the third round, the three bulbs are [on, off, off].
+    So you should return 1 because there is only one bulb is on.
+
+**Example 2:**
+
+    Input: n = 0
+    Output: 0
+
+**Example 3:**
+
+    Input: n = 1
+    Output: 1
+
+## 题目大意
+
+初始时有 n 个灯泡处于关闭状态。第一轮，你将会打开所有灯泡。接下来的第二轮，你将会每两个灯泡关闭一个。
+
+第三轮，你每三个灯泡就切换一个灯泡的开关（即，打开变关闭，关闭变打开）。第 i 轮，你每 i 个灯泡就切换一个灯泡的开关。直到第 n 轮，你只需要切换最后一个灯泡的开关。
+
+找出并返回 n 轮后有多少个亮着的灯泡。
+
+## 解题思路
+
+- 计算 1 到 n 中有奇数个约数的个数
+- 1 到 n 中的某个数 x 有奇数个约数,也即 x 是完全平方数
+- 计算 1 到 n 中完全平方数的个数 sqrt(n)
+
+## 代码
+
+```go
+
+package leetcode
+
+import "math"
+
+func bulbSwitch(n int) int {
+	return int(math.Sqrt(float64(n)))
+}
+
+```
+
+
+----------------------------------------------
+<div style="display: flex;justify-content: space-between;align-items: center;">
+<p><a href="https://books.halfrost.com/leetcode/ChapterFour/0300~0399/0318.Maximum-Product-of-Word-Lengths/">⬅️上一页</a></p>
+<p><a href="https://books.halfrost.com/leetcode/ChapterFour/0300~0399/0322.Coin-Change/">下一页➡️</a></p>
+</div>

website/content/ChapterFour/0300~0399/0319.Bulb-Switcher.md

@@ -63,6 +63,6 @@ func coinChange(coins []int, amount int) int {
 
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 <div style="display: flex;justify-content: space-between;align-items: center;">
-<p><a href="https://books.halfrost.com/leetcode/ChapterFour/0300~0399/0318.Maximum-Product-of-Word-Lengths/">⬅️上一页</a></p>
+<p><a href="https://books.halfrost.com/leetcode/ChapterFour/0300~0399/0319.Bulb-Switcher/">⬅️上一页</a></p>
 <p><a href="https://books.halfrost.com/leetcode/ChapterFour/0300~0399/0324.Wiggle-Sort-II/">下一页➡️</a></p>
 </div>

website/content/ChapterFour/0300~0399/0322.Coin-Change.md

@@ -138,5 +138,5 @@ func (p *pq) Pop() interface{} {
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 <div style="display: flex;justify-content: space-between;align-items: center;">
 <p><a href="https://books.halfrost.com/leetcode/ChapterFour/0300~0399/0377.Combination-Sum-IV/">⬅️上一页</a></p>
-<p><a href="https://books.halfrost.com/leetcode/ChapterFour/0300~0399/0385.Mini-Parser/">下一页➡️</a></p>
+<p><a href="https://books.halfrost.com/leetcode/ChapterFour/0300~0399/0384.Shuffle-an-Array/">下一页➡️</a></p>
 </div>

website/content/ChapterFour/0300~0399/0378.Kth-Smallest-Element-in-a-Sorted-Matrix.md

@@ -0,0 +1,89 @@
+# [384.Shuffle an Array](https://leetcode.com/problems/shuffle-an-array/)
+
+## 题目
+
+Given an integer array nums, design an algorithm to randomly shuffle the array. All permutations of the array should be equally likely as a result of the shuffling.
+
+Implement the Solution class:
+
+- Solution(int[] nums) Initializes the object with the integer array nums.
+- int[] reset() Resets the array to its original configuration and returns it.
+- int[] shuffle() Returns a random shuffling of the array.
+
+**Example 1**:
+
+    Input
+    ["Solution", "shuffle", "reset", "shuffle"]
+    [[[1, 2, 3]], [], [], []]
+    Output
+    [null, [3, 1, 2], [1, 2, 3], [1, 3, 2]]
+
+    Explanation
+    Solution solution = new Solution([1, 2, 3]);
+    solution.shuffle();    // Shuffle the array [1,2,3] and return its result.
+    // Any permutation of [1,2,3] must be equally likely to be returned.
+    // Example: return [3, 1, 2]
+    solution.reset();      // Resets the array back to its original configuration [1,2,3]. Return [1, 2, 3]
+    solution.shuffle();    // Returns the random shuffling of array [1,2,3]. Example: return [1, 3, 2]
+
+**Constraints:**
+
+- 1 <= nums.length <= 200
+- -1000000 <= nums[i] <= 1000000
+- All the elements of nums are unique.
+- At most 5 * 10000 calls in total will be made to reset and shuffle.
+
+## 题目大意
+
+给你一个整数数组 nums ，设计算法来打乱一个没有重复元素的数组。
+
+实现 Solution class:
+
+- Solution(int[] nums) 使用整数数组 nums 初始化对象
+- int[] reset() 重设数组到它的初始状态并返回
+- int[] shuffle() 返回数组随机打乱后的结果
+
+## 解题思路
+
+- 使用 rand.Shuffle 进行数组随机打乱
+
+## 代码
+
+```go
+
+package leetcode
+
+import "math/rand"
+
+type Solution struct {
+	nums []int
+}
+
+func Constructor(nums []int) Solution {
+	return Solution{
+		nums: nums,
+	}
+}
+
+/** Resets the array to its original configuration and return it. */
+func (this *Solution) Reset() []int {
+	return this.nums
+}
+
+/** Returns a random shuffling of the array. */
+func (this *Solution) Shuffle() []int {
+	arr := make([]int, len(this.nums))
+	copy(arr, this.nums)
+	rand.Shuffle(len(arr), func(i, j int) {
+		arr[i], arr[j] = arr[j], arr[i]
+	})
+	return arr
+}
+```
+
+
+----------------------------------------------
+<div style="display: flex;justify-content: space-between;align-items: center;">
+<p><a href="https://books.halfrost.com/leetcode/ChapterFour/0300~0399/0378.Kth-Smallest-Element-in-a-Sorted-Matrix/">⬅️上一页</a></p>
+<p><a href="https://books.halfrost.com/leetcode/ChapterFour/0300~0399/0385.Mini-Parser/">下一页➡️</a></p>
+</div>

website/content/ChapterFour/0300~0399/0384.Shuffle-an-Array.md

@@ -177,6 +177,6 @@ func deserialize(s string) *NestedInteger {
 
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 <div style="display: flex;justify-content: space-between;align-items: center;">
-<p><a href="https://books.halfrost.com/leetcode/ChapterFour/0300~0399/0378.Kth-Smallest-Element-in-a-Sorted-Matrix/">⬅️上一页</a></p>
+<p><a href="https://books.halfrost.com/leetcode/ChapterFour/0300~0399/0384.Shuffle-an-Array/">⬅️上一页</a></p>
 <p><a href="https://books.halfrost.com/leetcode/ChapterFour/0300~0399/0386.Lexicographical-Numbers/">下一页➡️</a></p>
 </div>