每日一题 - 2019-06-05 (azl397985856#29)

Author: WendyGeng

daily/2019-06-05.md

@@ -0,0 +1,108 @@
+## 每日一题 - Find All Numbers Disappeared in an Array
+
+### 信息卡片
+
+- 时间：2019-06-05
+- 题目链接：https://leetcode.com/problems/find-all-numbers-disappeared-in-an-array/
+- tag：`array`
+
+### 题目描述
+
+```
+Given an array of integers where 1 ≤ a[i] ≤ n (n = size of array), some elements appear twice and others appear once.
+
+Find all the elements of [1, n] inclusive that do not appear in this array.
+
+Could you do it without extra space and in O(n) runtime? You may assume the returned list does not count as extra space.
+
+Example:
+
+Input:
+[4,3,2,7,8,2,3,1]
+
+Output:
+[5,6]
+```
+
+### 参考答案
+
+#### 使用额外的空间记录出现过的数字, 时间复杂度和空间复杂度皆为O(n)
+
+参考代码
+```javascript
+/*
+ * @lc app=leetcode id=448 lang=javascript
+ *
+ * [448] Find All Numbers Disappeared in an Array
+ */
+/**
+ * @param {number[]} nums
+ * @return {number[]}
+ */
+var findDisappearedNumbers = function(nums) {
+    let allNums = [];
+    let res = [];
+
+    for (let i = 0; i < nums.length; i++){
+        allNums[nums[i] - 1] = true;
+    }
+
+    for (let i = 0; i < nums.length; i++){
+        if(!allNums[i]){
+            res.push(i + 1);
+        }
+    }
+    return res;
+};
+```
+
+#### 充分利用题目 "You may assume the returned list does not count as extra space."
+
+- 用res记录哪些数字出现过
+- 最后遍历时, 判断res是否为空, 若是, 则证明未出现过, 将其写回res
+
+参考代码
+```javascript
+/*
+ * @lc app=leetcode id=448 lang=javascript
+ *
+ * [448] Find All Numbers Disappeared in an Array
+ */
+/**
+ * @param {number[]} nums
+ * @return {number[]}
+ */
+var findDisappearedNumbers = function(nums) {
+    const res = [];
+    let cur = 0;
+    for(let i = 0; i < nums.length; i++) {
+        res[nums[i]] = true;
+    }
+
+    for(let i = 0; i < nums.length; i++) {
+        if (res[i + 1] === void 0) {
+            res[cur++] = i + 1;
+        }
+    }
+
+    res.length = cur;
+
+    return res;
+};
+```
+
+
+### 其他优秀解答
+利用python集合类型的特点： 元素唯一, 不存在相同元素
+
+```python
+class Solution(object):
+    def findDisappearedNumbers(self, nums):
+        """
+        :type nums: List[int]
+        :rtype: List[int]
+        """
+        ls = [i for i in range(1, len(nums)+1)]
+
+        return list(set(ls) - set(nums))
+```

daily/README.md

@@ -17,6 +17,12 @@ tag: `Array`
 
 时间: 2019-06-04
 
+#### [448.Find All Numbers Disappeared in an Array](./2019-06-05.md)
+
+tag: `Array`
+
+时间: 2019-06-05
+
 #### [617. Merge Two Binary Trees](./2019-06-10.md)
 
 tag: `Tree`