Merge pull request #193 from flames519/master

链表相关的19，142，202  JavaScript版本

problems/0019.删除链表的倒数第N个节点.md

@@ -135,6 +135,28 @@ func removeNthFromEnd(head *ListNode, n int) *ListNode {
 }
 ```
 
+JavaScript:
+
+```js
+/**
+ * @param {ListNode} head
+ * @param {number} n
+ * @return {ListNode}
+ */
+var removeNthFromEnd = function(head, n) {
+    let ret = new ListNode(0, head),
+        slow = fast = ret;
+    while(n--) fast = fast.next;
+    if(!fast) return ret.next;
+    while (fast.next) {
+        fast = fast.next; 
+        slow = slow.next
+    };
+    slow.next = slow.next.next;
+    return ret.next;
+};
+```
+
 -----------------------
 * 作者微信：[程序员Carl](https://mp.weixin.qq.com/s/b66DFkOp8OOxdZC_xLZxfw)
 * B站视频：[代码随想录](https://space.bilibili.com/525438321)

problems/0142.环形链表II.md

@@ -258,6 +258,50 @@ Go：
 }
 ```
 
+javaScript
+
+```js
+// 两种循环实现方式
+/**
+ * @param {ListNode} head
+ * @return {ListNode}
+ */
+// 先判断是否是环形链表
+var detectCycle = function(head) {
+    if(!head || !head.next) return null;
+    let slow =head.next, fast = head.next.next;
+    while(fast && fast.next && fast!== slow) {
+        slow = slow.next;
+        fast = fast.next.next; 
+    }
+    if(!fast || !fast.next ) return null;
+    slow = head;
+    while (fast !== slow) {
+        slow = slow.next;
+        fast = fast.next;
+    }
+    return slow;
+};
+
+var detectCycle = function(head) {
+    if(!head || !head.next) return null;
+    let slow =head.next, fast = head.next.next;
+    while(fast && fast.next) {
+        slow = slow.next;
+        fast = fast.next.next;
+        if(fast == slow) {
+            slow = head;
+            while (fast !== slow) {
+                slow = slow.next;
+                fast = fast.next;
+            }
+            return slow;
+        }
+    }
+    return null;
+};
+```
+
 
 -----------------------
 * 作者微信：[程序员Carl](https://mp.weixin.qq.com/s/b66DFkOp8OOxdZC_xLZxfw)

problems/0202.快乐数.md

@@ -112,6 +112,40 @@ Python：
 
 Go：
 
+javaScript:
+
+```js
+function getN(n) {
+    if (n == 1 || n == 0) return n;
+    let res = 0;
+    while (n) {
+        res += (n % 10) * (n % 10);
+        n = parseInt(n / 10);
+    }
+    return res;
+}
+
+var isHappy = function(n) {
+    const sumSet = new Set();
+    while (n != 1 && !sumSet.has(n)) {
+        sumSet.add(n);
+        n = getN(n);
+    }
+    return n == 1;
+};
+
+// 使用环形链表的思想 说明出现闭环 退出循环
+var isHappy = function(n) {
+    if (getN(n) == 1) return true;
+    let a = getN(n), b = getN(getN(n));
+    // 如果 a === b 
+    while (b !== 1 && getN(b) !== 1 && a !== b) {
+        a = getN(a);
+        b = getN(getN(b));
+    }
+    return b === 1 || getN(b) === 1 ;
+};
+```
 
 
 

problems/二叉树的迭代遍历.md

@@ -330,6 +330,70 @@ func inorderTraversal(root *TreeNode) []int {
 }
 ```
 
+javaScript
+
+```js
+
+前序遍历:
+
+// 入栈 右 -> 左
+// 出栈 中 -> 左 -> 右
+var preorderTraversal = function(root, res = []) {
+    if(!root) return res;
+    const stack = [root];
+    let cur = null;
+    while(stack.length) {
+        cur = stack.pop();
+        res.push(cur.val);
+        cur.right && stack.push(cur.right);
+        cur.left && stack.push(cur.left);
+    }
+    return res;
+};
+
+中序遍历:
+
+// 入栈 左 -> 右
+// 出栈 左 -> 中 -> 右
+
+var inorderTraversal = function(root, res = []) {
+    const stack = [];
+    let cur = root;
+    while(stack.length || cur) {
+        if(cur) {
+            stack.push(cur);
+            // 左
+            cur = cur.left;
+        } else {
+            // --> 弹出 中
+            cur = stack.pop();
+            res.push(cur.val); 
+            // 右
+            cur = cur.right;
+        }
+    };
+    return res;
+};
+
+后序遍历:
+
+// 入栈 左 -> 右
+// 出栈 中 -> 右 -> 左 结果翻转
+
+var postorderTraversal = function(root, res = []) {
+    if (!root) return res;
+    const stack = [root];
+    let cur = null;
+    do {
+        cur = stack.pop();
+        res.push(cur.val);
+        cur.left && stack.push(cur.left);
+        cur.right && stack.push(cur.right);
+    } while(stack.length);
+    return res.reverse();
+};
+```
+
 
 -----------------------
 * 作者微信：[程序员Carl](https://mp.weixin.qq.com/s/b66DFkOp8OOxdZC_xLZxfw)

problems/二叉树的递归遍历.md

@@ -272,6 +272,41 @@ func PostorderTraversal(root *TreeNode) (res []int) {
 }
 ```
 
+javaScript:
+
+```js
+
+前序遍历:
+
+var preorderTraversal = function(root, res = []) {
+    if (!root) return res;
+    res.push(root.val);
+    preorderTraversal(root.left, res)
+    preorderTraversal(root.right, res)
+    return res;
+};
+
+中序遍历:
+
+var inorderTraversal = function(root, res = []) {
+    if (!root) return res;
+    inorderTraversal(root.left, res);
+    res.push(root.val);
+    inorderTraversal(root.right, res);
+    return res;
+};
+
+后序遍历:
+
+var postorderTraversal = function(root, res = []) {
+    if (!root) return res;
+    postorderTraversal(root.left, res);
+    postorderTraversal(root.right, res);
+    res.push(root.val);
+    return res;
+};
+```
+