note

Author: guangxush

guangxu/202107/20210701.md

@@ -1,11 +1,89 @@
 ## Algorithm
 
+[151. Reverse Words in a String](https://leetcode.com/problems/reverse-words-in-a-string/)
+
 ### Description
 
-### Solution
+Given an input string s, reverse the order of the words.
+
+A word is defined as a sequence of non-space characters. The words in s will be separated by at least one space.
+
+Return a string of the words in reverse order concatenated by a single space.
+
+Note that s may contain leading or trailing spaces or multiple spaces between two words. The returned string should only have a single space separating the words. Do not include any extra spaces.
+
+
+Example 1:
+
+```
+Input: s = "the sky is blue"
+Output: "blue is sky the"
+```
+
+Example 2:
+
+```
+Input: s = "  hello world  "
+Output: "world hello"
+Explanation: Your reversed string should not contain leading or trailing spaces.
+```
+
+Example 3:
 
-```java 
+```
+Input: s = "a good   example"
+Output: "example good a"
+Explanation: You need to reduce multiple spaces between two words to a single space in the reversed string.
+```
+
+Example 4:
+
+```
+Input: s = "  Bob    Loves  Alice   "
+Output: "Alice Loves Bob"
+```
+
+Example 5:
+
+```
+Input: s = "Alice does not even like bob"
+Output: "bob like even not does Alice"
+```
+
+Constraints:
+
+- 1 <= s.length <= 104
+- s contains English letters (upper-case and lower-case), digits, and spaces ' '.
+- There is at least one word in s.
+
+Follow-up: If the string data type is mutable in your language, can you solve it in-place with O(1) extra space?
+
+### Solution
 
+```java
+class Solution {
+    public String reverseWords(String s) {
+        Stack<String> stack = new Stack<>();
+        String temp = "";
+        for(int i=0;i<s.length();i++){
+            if(s.charAt(i)==' '&&temp.length()!=0){
+                stack.push(temp);
+                temp = "";
+            }else if(s.charAt(i)!=' '){
+                temp += s.charAt(i);
+            }
+            if(i==s.length()-1){
+                stack.push(temp.trim());
+            }
+        }
+        String result = "";
+        while(!stack.isEmpty()){
+            result += stack.pop();
+            result += " ";
+        }
+        return result.strip();
+    }
+}
 ```
 
 ### Discuss

guangxu/202107/20210702.md

@@ -1,11 +1,73 @@
 ## Algorithm
 
+[287. Find the Duplicate Number](https://leetcode.com/problems/find-the-duplicate-number/)
+
 ### Description
 
-### Solution
+Given an array of integers nums containing n + 1 integers where each integer is in the range [1, n] inclusive.
+
+There is only one repeated number in nums, return this repeated number.
+
+You must solve the problem without modifying the array nums and uses only constant extra space.
+
+
+Example 1:
+
+```
+Input: nums = [1,3,4,2,2]
+Output: 2
+```
+
+Example 2:
+
+```
+Input: nums = [3,1,3,4,2]
+Output: 3
+```
 
-```java 
+Example 3:
+
+```
+Input: nums = [1,1]
+Output: 1
+```
+
+Example 4:
+
+```
+Input: nums = [1,1,2]
+Output: 1
+```
+
+Constraints:
+
+- 1 <= n <= 105
+- nums.length == n + 1
+- 1 <= nums[i] <= n
+- All the integers in nums appear only once except for precisely one integer which appears two or more times.
+
+Follow up:
+
+- How can we prove that at least one duplicate number must exist in nums?
+- Can you solve the problem in linear runtime complexity?
+
+### Solution
 
+```java
+class Solution {
+    public int findDuplicate(int[] nums) {
+        int[] duplicate = new int[nums.length];
+        for(int i=0;i<nums.length;i++){
+            duplicate[nums[i]]++;
+        }
+        for(int i=0;i<duplicate.length;i++){
+            if(duplicate[i]>1){
+                return i;
+            }
+        }
+        return -1;
+    }
+}
 ```
 
 ### Discuss

guangxu/README.md

@@ -1,5 +1,7 @@
 | 标题 | Algorithm | Review | Tip | Share|
 | - | - | - | - | - |
+| [20210701](./202107/20210702.md) |[287. Find the Duplicate Number(发现数组中重复的数字)](https://leetcode.com/problems/find-the-duplicate-number/)||||
+| [20210701](./202107/20210701.md) |[151. Reverse Words in a String(翻转字符串里的单词)](https://leetcode.com/problems/reverse-words-in-a-string/)||||
 | [20210630](./202106/20210630.md) |[135. Candy(分发糖果)](https://leetcode.com/problems/candy/)||||
 | [20210629](./202106/20210629.md) |[129. Sum Root to Leaf Numbers(求根到叶子节点数字之和)](https://leetcode.com/problems/sum-root-to-leaf-numbers/)||||
 | [20210628](./202106/20210628.md) |[670. Maximum Swap(数组中两个数的最大异或值)](https://leetcode.com/problems/maximum-swap/)||||