Merge pull request #254 from xllpiupiu/master

0222完全二叉树的节点个数JavaScript版本

Author: youngyangyang04

problems/0222.完全二叉树的节点个数.md

@@ -243,6 +243,74 @@ Python：
 
 Go：
 
+JavaScript:
+
+递归版本
+```javascript
+var countNodes = function(root) {
+    //递归法计算二叉树节点数
+    // 1. 确定递归函数参数
+    const getNodeSum=function(node){
+    //2. 确定终止条件
+        if(node===null){
+            return 0;
+        }
+    //3. 确定单层递归逻辑
+        let leftNum=getNodeSum(node.left);
+        let rightNum=getNodeSum(node.right);
+        return leftNum+rightNum+1;
+    }
+    return getNodeSum(root);
+};
+```
+
+迭代(层序遍历)版本
+```javascript
+var countNodes = function(root) {
+    //层序遍历
+    let queue=[];
+    if(root===null){
+        return 0;
+    }
+    queue.push(root);
+    let nodeNums=0;
+    while(queue.length){
+        let length=queue.length;
+        while(length--){
+            let node=queue.shift();
+            nodeNums++;
+            node.left&&queue.push(node.left);
+            node.right&&queue.push(node.right);
+        }
+    }
+    return nodeNums;
+};
+```
+
+利用完全二叉树性质 
+```javascript
+var countNodes = function(root) {
+    //利用完全二叉树的特点
+    if(root===null){
+        return 0;
+    }
+    let left=root.left;
+    let right=root.right;
+    let leftHeight=0,rightHeight=0;
+    while(left){
+        left=left.left;
+        leftHeight++;
+    }
+    while(right){
+        right=right.right;
+        rightHeight++;
+    }
+    if(leftHeight==rightHeight){
+        return Math.pow(2,leftHeight+1)-1;
+    }
+    return countNodes(root.left)+countNodes(root.right)+1;
+};
+```