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docs: add No13、53、191、384题解
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‎leetcode刷题/README.md

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- [No.1 两数之和](https://github.com/Mayandev/javascript_algorithm/blob/master/leetcode%E5%88%B7%E9%A2%98/note/No1_two-sum.md)
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- [No.7 整数反转](https://github.com/Mayandev/javascript_algorithm/blob/master/leetcode%E5%88%B7%E9%A2%98/note/No7_reverse.md)
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- [No.8 字符串转换整数 (atoi)](https://github.com/Mayandev/javascript_algorithm/blob/master/leetcode%E5%88%B7%E9%A2%98/note/No8_my-atoi.md)
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- [No.13 罗马数字转整数](note/No13_roman-to-int.md)
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- [No.14 最长公共前缀](https://github.com/Mayandev/javascript_algorithm/blob/master/leetcode%E5%88%B7%E9%A2%98/note/No14_longest-common-prefix.md)
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- [No.19 删除链表倒数第 n 个节点](https://github.com/Mayandev/javascript_algorithm/blob/master/leetcode%E5%88%B7%E9%A2%98/note/No19_remove-nth-from-end.md)
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- [No.20 有效的括号](https://github.com/Mayandev/javascript_algorithm/blob/master/leetcode%E5%88%B7%E9%A2%98/note/No20_is-valid.md)
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- [No.36 有效的数独](https://github.com/Mayandev/javascript_algorithm/blob/master/leetcode%E5%88%B7%E9%A2%98/note/No36_isvalid-sudoku.md)
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- [No.38 报数](https://github.com/Mayandev/javascript_algorithm/blob/master/leetcode%E5%88%B7%E9%A2%98/note/No38_count-and-say.md)
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- [No.48 旋转图像](https://github.com/Mayandev/javascript_algorithm/blob/master/leetcode%E5%88%B7%E9%A2%98/note/No48_rotate.md)
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- [No.53 最大子序和](note/No53_max-sub-array.md)
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- [No.66 加一](https://github.com/Mayandev/javascript_algorithm/blob/master/leetcode%E5%88%B7%E9%A2%98/note/No66_plus-one.md)
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- [No.70 爬楼梯](https://github.com/Mayandev/javascript_algorithm/blob/master/leetcode%E5%88%B7%E9%A2%98/note/No70_climb-stairs.md)
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- [No.88 合并两个有序数组](https://github.com/Mayandev/javascript_algorithm/blob/master/leetcode%E5%88%B7%E9%A2%98/note/No88_merge.md)
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- [No.160 相交链表](https://github.com/Mayandev/javascript_algorithm/blob/master/leetcode%E5%88%B7%E9%A2%98/note/No160_get-intersection-node.md)
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- [No.169 多数元素](https://github.com/Mayandev/javascript_algorithm/blob/master/leetcode%E5%88%B7%E9%A2%98/note/No169_majority-element.md)
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- [No.189 旋转数组](https://github.com/Mayandev/javascript_algorithm/blob/master/leetcode%E5%88%B7%E9%A2%98/note/No189_rotate-arr.md)
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- [No.191 位1的个数](note/No191_hamming-weight.md)
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- [No.198 打家劫舍](https://github.com/Mayandev/javascript_algorithm/blob/master/leetcode%E5%88%B7%E9%A2%98/note/No198_rob.md)
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- [No.204 计数质数](https://github.com/Mayandev/javascript_algorithm/blob/master/leetcode%E5%88%B7%E9%A2%98/note/No204_count-primes.md)
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- [No.206 反转链表](https://github.com/Mayandev/javascript_algorithm/blob/master/leetcode%E5%88%B7%E9%A2%98/note/No206_reverse-list.md)
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- [No.283 移动零](https://github.com/Mayandev/javascript_algorithm/blob/master/leetcode%E5%88%B7%E9%A2%98/note/No283_move-zeroes.md)
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- [No.326 3的幂](https://github.com/Mayandev/javascript_algorithm/blob/master/leetcode%E5%88%B7%E9%A2%98/note/No326_is-power-of-three.md)
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- [No.350 两个数组的交集 II](https://github.com/Mayandev/javascript_algorithm/blob/master/leetcode%E5%88%B7%E9%A2%98/note/No350_intersect.md)
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- [No.384 打乱数组](note/No384_shuffle.md)
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- [No.387 字符串中的第一个唯一字符](https://github.com/Mayandev/javascript_algorithm/blob/master/leetcode%E5%88%B7%E9%A2%98/note/No387_first-uniq-char.md)
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- [No.412 Fizz Buzz](https://github.com/Mayandev/javascript_algorithm/blob/master/leetcode%E5%88%B7%E9%A2%98/note/No412_fizz-buzz.md)
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- [No.448 找到所有数组中消失的数字](https://github.com/Mayandev/javascript_algorithm/blob/master/leetcode%E5%88%B7%E9%A2%98/note/No448_find-disappeared-numbers.md)
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#### 数学初级
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- [No.13 罗马数字转整数](note/No13_roman-to-int.md)
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- [No.326 3的幂](https://github.com/Mayandev/javascript_algorithm/blob/master/leetcode%E5%88%B7%E9%A2%98/note/No326_is-power-of-three.md)
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- [No.204 计数质数](https://github.com/Mayandev/javascript_algorithm/blob/master/leetcode%E5%88%B7%E9%A2%98/note/No204_count-primes.md)
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- [No.492 构造矩形](https://github.com/Mayandev/javascript_algorithm/blob/master/leetcode%E5%88%B7%E9%A2%98/note/No492_construct-rectangle.md)
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### 动态规划
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- [No.53 最大子序和](note/No53_max-sub-array.md)
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- [No.70 爬楼梯](https://github.com/Mayandev/javascript_algorithm/blob/master/leetcode%E5%88%B7%E9%A2%98/note/No70_climb-stairs.md)
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- [No.121 买卖股票的最佳时机](https://github.com/Mayandev/javascript_algorithm/blob/master/leetcode%E5%88%B7%E9%A2%98/note/No121_max-profit.md)
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- [No.198 打家劫舍](https://github.com/Mayandev/javascript_algorithm/blob/master/leetcode%E5%88%B7%E9%A2%98/note/No198_rob.md)
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### 排序和搜索
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- [No.88 合并两个有序数组](https://github.com/Mayandev/javascript_algorithm/blob/master/leetcode%E5%88%B7%E9%A2%98/note/No88_merge.md)
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# No.13 罗马数字转整数
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难度:`easy`
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罗马数字包含以下七种字符: I, V, X, L,C,D 和 M。
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字符 数值
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I 1
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V 5
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X 10
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L 50
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C 100
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D 500
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M 1000
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例如, 罗马数字 2 写做 II ,即为两个并列的 1。12 写做 XII ,即为 X + II 。 27 写做 XXVII, 即为 XX + V + II 。
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通常情况下,罗马数字中小的数字在大的数字的右边。但也存在特例,例如 4 不写做 IIII,而是 IV。数字 1 在数字 5 的左边,所表示的数等于大数 5 减小数 1 得到的数值 4 。同样地,数字 9 表示为 IX。这个特殊的规则只适用于以下六种情况:
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```
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I 可以放在 V (5) 和 X (10) 的左边,来表示 4 和 9。
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X 可以放在 L (50) 和 C (100) 的左边,来表示 40 和 90。
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C 可以放在 D (500) 和 M (1000) 的左边,来表示 400 和 900。
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给定一个罗马数字,将其转换成整数。输入确保在 1 到 3999 的范围内。
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```
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## 示例
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示例 1:
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```
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输入: "III"
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输出: 3
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```
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示例 2:
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```
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输入: "IV"
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输出: 4
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```
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示例 3:
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```
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输入: "IX"
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输出: 9
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```
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示例 4:
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```
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输入: "LVIII"
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输出: 58
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解释: L = 50, V= 5, III = 3.
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```
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示例 5:
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```
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输入: "MCMXCIV"
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输出: 1994
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解释: M = 1000, CM = 900, XC = 90, IV = 4.
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```
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## 解题思路
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先建立一个HashMap来映射符号和值,然后对字符串从左到右来,如果当前字符代表的值不小于其右边,就加上该值;否则就减去该值。以此类推到最左边的数,最终得到的结果即是答案。
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代码如下:
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```javascript
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/**
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* @param {string} s
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* @return {number}
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*/
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var romanToInt = function(s) {
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let map = {
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'I': 1,
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'V': 5,
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'X': 10,
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'L': 50,
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'C': 100,
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'D': 500,
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'M': 1000,
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}
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let num = 0;
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let n = s.length;
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for (let i = 0; i < n; i++) {
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if (map[s[i]]<map[s[i+1]] && i < n-1) {
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num -= map[s[i]];
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} else {
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num += map[s[i]];
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}
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console.log(num);
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}
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return num;
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};
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```
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# No.191 位1的个数
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编写一个函数,输入是一个无符号整数,返回其二进制表达式中数字位数为 ‘1’ 的个数(也被称为汉明重量)。
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## 示例
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示例 1:
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```
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输入:00000000000000000000000000001011
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输出:3
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解释:输入的二进制串 00000000000000000000000000001011 中,共有三位为 '1'。
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```
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示例 2:
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```
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输入:00000000000000000000000010000000
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输出:1
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解释:输入的二进制串 00000000000000000000000010000000 中,共有一位为 '1'。
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```
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示例 3:
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```
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输入:11111111111111111111111111111101
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输出:31
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解释:输入的二进制串 11111111111111111111111111111101 中,共有 31 位为 '1'。
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```
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## 解题思路
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代码如下:
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```javascript
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/**
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* @param {number} n - a positive integer
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* @return {number}
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*/
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var hammingWeight = function(n) {
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let count = 0;
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let mask = 1;
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for(let i = 0;i < 32;i++){
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if((n & mask) != 0){
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count++;
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}
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mask <<= 1;
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}
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return count;
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};
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```

‎leetcode刷题/note/No384_shuffle.md

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# No.384 打乱数组
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难度:`middle`
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打乱一个没有重复元素的数组。
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## 示例
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示例:
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```
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// 以数字集合 1, 2 和 3 初始化数组。
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int[] nums = {1,2,3};
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Solution solution = new Solution(nums);
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// 打乱数组 [1,2,3] 并返回结果。任何 [1,2,3]的排列返回的概率应该相同。
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solution.shuffle();
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// 重设数组到它的初始状态[1,2,3]。
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solution.reset();
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// 随机返回数组[1,2,3]打乱后的结果。
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solution.shuffle();
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```
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## 解题思路
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主要是乱序到方法,可以使用洗牌算法,一边遍历数组,遍历的同时随机生成一个下标,将当前遍历的下标与随机生成的下标元素进行交换。
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代码如下:
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```javascript
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/**
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* @param {number[]} nums
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*/
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var Solution = function(nums) {
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this.nums = nums;
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this.original = [...nums];
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};
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/**
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* Resets the array to its original configuration and return it.
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* @return {number[]}
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*/
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Solution.prototype.reset = function() {
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return this.original;
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};
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/**
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* Returns a random shuffling of the array.
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* @return {number[]}
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*/
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Solution.prototype.shuffle = function() {
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// 洗牌算法,一边遍历数组,遍历的同时随机生成一个下标,将当前遍历的下标与随机生成的下标元素进行交换
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for (let i = 0, n = this.nums.length; i < n; i++) {
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let randomIdx = Math.floor(Math.random()*n);
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let temp = this.nums[i];
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this.nums[i] = this.nums[randomIdx];
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this.nums[randomIdx] = temp;
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}
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return this.nums;
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};
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/**
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* Your Solution object will be instantiated and called as such:
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* var obj = new Solution(nums)
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* var param_1 = obj.reset()
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* var param_2 = obj.shuffle()
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*/
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```
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‎leetcode刷题/note/No53_max-sub-array.md

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**思路二:**
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动态规划,一遍遍历,每次遍历计算出。类似寻找最大最小值的题目,初始值一定要定义成理论上的最小最大值
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动态规划,一遍遍历,每次遍历计算出。类似寻找最大最小值的题目,初始值一定要定义成理论上的最小最大值。
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遍历到当前数时,看是否有增益效果,并计算出当前到最大值。
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代码如下:
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```javascript
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/**
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* @param {number[]} nums
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* @return {number}
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*/
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var maxSubArray = function(nums) {
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let ans = nums[0];
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let sum = 0;
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for(let num of nums) {
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if(sum > 0) {
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sum += num;
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} else {
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sum = num;
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}
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ans = Math.max(ans, sum);
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}
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return ans;
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};
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```

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