diff --git a/.vscode/settings.json b/.vscode/settings.json
index 38e1d7b..7d8629b 100644
--- a/.vscode/settings.json
+++ b/.vscode/settings.json
@@ -1,10 +1,18 @@
 {
   "cSpell.words": [
+    "abcdefg",
+    "cdefgab",
+    "chuan",
     "dvdf",
     "lcci",
     "lcof",
+    "lrloseumgh",
+    "mincost",
     "nums",
     "pwwkew",
-    "zhong"
+    "umghlrlose",
+    "xuan",
+    "zhong",
+    "zhuan"
   ]
 }
\ No newline at end of file
diff --git a/README.md b/README.md
index 8ab20ce..f9d24c5 100644
--- a/README.md
+++ b/README.md
@@ -67,6 +67,10 @@ LeetCode 与 LintCode 解题记录。此为个人练习仓库，代码中对重
 
   - 面试题参考思路，不严谨实现 廖雪峰 不要使用JavaScript内置的parseInt()函数，利用map和reduce操作实现一个string2int()函数。 https://www.liaoxuefeng.com/wiki/1022910821149312/1024322552460832
 
+- [左旋转字符串](src/string/zuo-xuan-zhuan-zi-fu-chuan-lcof.js)
+
+  - LeetCode 面试题58 - II. 左旋转字符串 https://leetcode-cn.com/problems/zuo-xuan-zhuan-zi-fu-chuan-lcof/
+
 ## 数组
 
 - [电话号码的字母组合](src/array/letter-combinations-of-a-phone-number.js)
@@ -253,7 +257,16 @@ LeetCode 与 LintCode 解题记录。此为个人练习仓库，代码中对重
 
 - [最大数和最小数](src/array/maximum-and-minimum.js)
 
-  LintCode 770. 最大数和最小数 https://www.lintcode.com/problem/maximum-and-minimum/description
+  - LintCode 770. 最大数和最小数 https://www.lintcode.com/problem/maximum-and-minimum/description
+
+- [最低票价](src/array/minimum-cost-for-tickets.js)
+
+  - LeetCode 983. 最低票价 https://leetcode-cn.com/problems/minimum-cost-for-tickets/
+
+- [最大正方形](src/array/maximal-square.js)
+
+  - LeetCode 221. 最大正方形 https://leetcode-cn.com/problems/maximal-square/
+  - LintCode 436. 最大正方形 https://www.lintcode.com/problem/maximal-square/description
 
 ## 栈
 
@@ -310,6 +323,11 @@ LeetCode 与 LintCode 解题记录。此为个人练习仓库，代码中对重
   - LeetCode 236. 二叉树的最近公共祖先 https://leetcode-cn.com/problems/lowest-common-ancestor-of-a-binary-tree/
   - LintCode 88. 最近公共祖先 https://www.lintcode.com/problem/lowest-common-ancestor-of-a-binary-tree/description
 
+- [另一个树的子树](src/tree/subtree-of-another-tree.js)
+
+  - LeetCode 572. 另一个树的子树 https://leetcode-cn.com/problems/subtree-of-another-tree/
+  - LintCode 1165. 另一个树的子树 https://www.lintcode.com/problem/subtree-of-another-tree/description
+
 ## 链表
 
 - [合并K个排序链表](src/list/merge-k-sorted-lists.js)
@@ -320,9 +338,15 @@ LeetCode 与 LintCode 解题记录。此为个人练习仓库，代码中对重
 - [合并两个有序链表](src/list/merge-two-sorted-lists.js)
 
   - LeetCode 21. 合并两个有序链表 https://leetcode-cn.com/problems/merge-two-sorted-lists/
+  - LeetCode 面试题25. 合并两个排序的链表 https://leetcode-cn.com/problems/he-bing-liang-ge-pai-xu-de-lian-biao-lcof
   - LintCode 165. 合并两个排序链表 https://www.lintcode.com/problem/merge-two-sorted-lists/description
 
 - [链表排序](src/list/sort-list.js)
 
   - LeetCode 148. 排序链表 https://leetcode-cn.com/problems/sort-list/
   - LintCode 98. 链表排序 https://www.lintcode.com/problem/sort-list/description
+
+- [环形链表](src/list/linked-list-cycle.js)
+
+  - LeetCode 141. 环形链表 https://leetcode-cn.com/problems/linked-list-cycle/
+  - LintCode 102. 带环链表 https://www.lintcode.com/problem/linked-list-cycle/description
diff --git a/src/array/maximal-square.js b/src/array/maximal-square.js
new file mode 100644
index 0000000..233441f
--- /dev/null
+++ b/src/array/maximal-square.js
@@ -0,0 +1,25 @@
+/**
+ * @param {character[][]} matrix
+ * @return {number}
+ */
+export const maximalSquare = function (matrix) {
+  if (!matrix || !matrix[0]) return 0
+
+  const rows = matrix.length
+  const cols = matrix[0].length
+  let max = 0
+
+  const dp = new Array(rows).fill().map(_ => new Array(cols).fill(0))
+
+  for (let n = 0; n < rows; n++) {
+    for (let i = 0; i < cols; i++) {
+      if (Number(matrix[n][i]) === 1) {
+        if (n === 0 || i === 0) dp[n][i] = 1
+        else dp[n][i] = Math.min(dp[n - 1][i], dp[n][i - 1], dp[n - 1][i - 1]) + 1 // 找规律
+        max = Math.max(max, dp[n][i])
+      }
+    }
+  }
+
+  return max * max
+}
diff --git a/src/array/minimum-cost-for-tickets.js b/src/array/minimum-cost-for-tickets.js
new file mode 100644
index 0000000..ab2d320
--- /dev/null
+++ b/src/array/minimum-cost-for-tickets.js
@@ -0,0 +1,43 @@
+/**
+ * @param {number[]} days
+ * @param {number[]} costs
+ * @return {number}
+ */
+export const mincostTickets = function (days, costs) {
+  //   动态规划:
+  //   dp[i]: 从第i天开始，到最后一天所用的票价总和
+
+  //   思路：
+  //   1. 记录数组中的最早的一天和最后的一天，动态规划从最后一天向前到最早一天即可，因为
+  //      其他时间不需要消耗通行证
+  //   2. 用一个变量 k 指针从 days 的最后一个索引向前走，i 指针也从最后一天向前走，但是遇到了
+  //      不需要花费通行证的某些天走 else 分支即可，即后一天的总花费就是这一天的总花费
+  //   3. 如果遇到需要通行证的时候，分别对比买一天、七天、三十天、所需的总花费，选择总花费最少的策略即可
+  //   4. 初始化的时候 dp 数组多了 30，是为了简化有的用例第 365 天需要出行，选择买 30 天
+  //      通行证的时候的特判
+
+  // 作者：ignore_express
+  // 链接：https://leetcode-cn.com/problems/minimum-cost-for-tickets/solution/js-dong-tai-gui-hua-si-lu-jiang-jie-by-ignore_expr/
+  // 来源：力扣（LeetCode）
+  // 著作权归作者所有。商业转载请联系作者获得授权，非商业转载请注明出处。
+  const dp = new Array(366 + 30).fill(0)
+  const n = days.length
+  const maxDay = days[n - 1]
+  const minDay = days[0]
+  let k = n - 1
+
+  for (let i = maxDay; i >= minDay; i--) {
+    if (i === days[k]) {
+      dp[i] = Math.min(
+        dp[i + 1] + costs[0],
+        dp[i + 7] + costs[1],
+        dp[i + 30] + costs[2]
+      )
+      k--
+    } else {
+      dp[i] = dp[i + 1]
+    }
+  }
+
+  return dp[minDay]
+}
diff --git a/src/list/linked-list-cycle.js b/src/list/linked-list-cycle.js
new file mode 100644
index 0000000..3459839
--- /dev/null
+++ b/src/list/linked-list-cycle.js
@@ -0,0 +1,28 @@
+/**
+ * Definition for singly-linked list.
+ * function ListNode(val) {
+ *     this.val = val;
+ *     this.next = null;
+ * }
+ */
+
+/**
+ * @param {ListNode} head
+ * @return {boolean}
+ */
+export const hasCycle = function (head) {
+  if (!head || !head.next) return false
+
+  // 双指针解法
+  let slow = head
+  let fast = head.next
+
+  while (true) {
+    if (!fast || !fast.next) return false
+    else if (fast.next === slow || fast === slow) return true
+    else {
+      fast = fast.next.next
+      slow = slow.next
+    }
+  }
+}
diff --git a/src/string/zuo-xuan-zhuan-zi-fu-chuan-lcof.js b/src/string/zuo-xuan-zhuan-zi-fu-chuan-lcof.js
new file mode 100644
index 0000000..de51a37
--- /dev/null
+++ b/src/string/zuo-xuan-zhuan-zi-fu-chuan-lcof.js
@@ -0,0 +1,8 @@
+/**
+ * @param {string} s
+ * @param {number} n
+ * @return {string}
+ */
+export const reverseLeftWords = function (s, n) {
+  return (s + s).substr(n, s.length)
+}
diff --git a/src/tree/subtree-of-another-tree.js b/src/tree/subtree-of-another-tree.js
new file mode 100644
index 0000000..121578b
--- /dev/null
+++ b/src/tree/subtree-of-another-tree.js
@@ -0,0 +1,27 @@
+/**
+ * Definition for a binary tree node.
+ * function TreeNode(val, left, right) {
+ *     this.val = (val===undefined ? 0 : val)
+ *     this.left = (left===undefined ? null : left)
+ *     this.right = (right===undefined ? null : right)
+ * }
+ */
+/**
+ * @param {TreeNode} s
+ * @param {TreeNode} t
+ * @return {boolean}
+ */
+export const isSubtree = function (s, t) {
+  if (!s && t) {
+    return false
+  }
+
+  const linkNode = function (node, target) {
+    if ((!node && target) || (node && !target)) return false
+    if (!node && !target) return true
+
+    return node.val === target.val ? linkNode(node.left, target.left) && linkNode(node.right, target.right) : false
+  }
+
+  return linkNode(s, t) || isSubtree(s.left, t) || isSubtree(s.right, t)
+}
diff --git a/test/array/maximal-square.test.js b/test/array/maximal-square.test.js
new file mode 100644
index 0000000..3e31906
--- /dev/null
+++ b/test/array/maximal-square.test.js
@@ -0,0 +1,15 @@
+import { maximalSquare } from '../../src/array/maximal-square'
+
+test('最大正方形', () => {
+  expect(maximalSquare([
+    [1, 0, 1, 0, 0],
+    [1, 0, 1, 1, 1],
+    [1, 1, 1, 1, 1],
+    [1, 0, 0, 1, 0]
+  ])).toBe(4)
+
+  expect(maximalSquare([
+    [0, 0, 0],
+    [1, 1, 1]
+  ])).toBe(1)
+})
diff --git a/test/array/minimum-cost-for-tickets.test.js b/test/array/minimum-cost-for-tickets.test.js
new file mode 100644
index 0000000..97ed54a
--- /dev/null
+++ b/test/array/minimum-cost-for-tickets.test.js
@@ -0,0 +1,6 @@
+import { mincostTickets } from '../../src/array/minimum-cost-for-tickets'
+
+test('最低票价', () => {
+  expect(mincostTickets([1, 4, 6, 7, 8, 20], [2, 7, 15])).toBe(11)
+  expect(mincostTickets([1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 30, 31], [2, 7, 15])).toBe(17)
+})
diff --git a/test/list/linked-list-cycle.test.js b/test/list/linked-list-cycle.test.js
new file mode 100644
index 0000000..abcf7c1
--- /dev/null
+++ b/test/list/linked-list-cycle.test.js
@@ -0,0 +1,24 @@
+import { hasCycle } from '../../src/list/linked-list-cycle'
+
+function ListNode (val) {
+  this.val = val
+  this.next = null
+}
+
+const arrToList = (arr) => {
+  const head = new ListNode(arr[0])
+  let current = head
+  for (let n = 1, len = arr.length; n < len; n++) {
+    current.next = new ListNode(arr[n])
+    current = current.next
+  }
+
+  return head
+}
+
+test('环形链表', () => {
+  const list = arrToList([1, 2, 3])
+  list.next.next.next = list
+  expect(hasCycle(list)).toBe(true)
+  expect(hasCycle(arrToList([1, 2, 3]))).toBe(false)
+})
diff --git a/test/string/zuo-xuan-zhuan-zi-fu-chuan-lcof.test.js b/test/string/zuo-xuan-zhuan-zi-fu-chuan-lcof.test.js
new file mode 100644
index 0000000..43c52de
--- /dev/null
+++ b/test/string/zuo-xuan-zhuan-zi-fu-chuan-lcof.test.js
@@ -0,0 +1,6 @@
+import { reverseLeftWords } from '../../src/string/zuo-xuan-zhuan-zi-fu-chuan-lcof'
+
+test('左旋转字符串', () => {
+  expect(reverseLeftWords('abcdefg', 2)).toBe('cdefgab')
+  expect(reverseLeftWords('lrloseumgh', 6)).toBe('umghlrlose')
+})
diff --git a/test/tree/subtree-of-another-tree.test.js b/test/tree/subtree-of-another-tree.test.js
new file mode 100644
index 0000000..bb54e19
--- /dev/null
+++ b/test/tree/subtree-of-another-tree.test.js
@@ -0,0 +1,7 @@
+import { isSubtree } from '../../src/tree/subtree-of-another-tree'
+import Tree from './Tree'
+
+test('另一个树的子树', () => {
+  expect(isSubtree(Tree.arrToTree([3, 4, 5, 1, 2]), Tree.arrToTree([4, 1, 2]))).toBe(true)
+  expect(isSubtree(Tree.arrToTree([3, 4, 5, 1, 2, null, null, null, null, 0]), Tree.arrToTree([4, 1, 2]))).toBe(false)
+})