Update 49 2022 0920 CTCI 2nd.md

Author: the-yuyut

紀錄/49 2022 0920 CTCI 2nd.md

@@ -28,3 +28,70 @@ This section covers how to prepare for technical questions (without wasting your
 * What Good Coding Looks Like
 * Don’t Give Up!**  
 
+---
+
+1. Listen
+2. Example
+3. Brute Force
+4. Optimize (BUD)
+5. Walk Through
+6. Implement
+7. Tests
+
+--- 
+
+2 sums 
+In a array return the indexes, which sum is T
+Z, not sorted, no duplicate, only 1, if no then empty/null
+
+---
+
+Yu
+
+1. Listen
+    1. N or Z, Sorted or not, duplicate, only 1 answer
+
+2. [n,n,n,], 0
+3. 兩兩排列組合，交換率減少重複
+4. 當前的數必定有一對應差值，我們將其記憶下來，一旦出現對應差值時則必有解，唯獨解不是差值而是相對應的 index，所以必須要有 mapping 的表
+
+
+5. walk through
+```
+when visit a index 
+if I know the element of index is a some diff number
+then the result is the mapping index and current index
+else I memerize the diff n and mapping its index.
+```
+
+map d
+
+7. 
+
+--- 
+
+Louis
+
+1. If no sum is T, then?
+2. Example
+[1,2,3], 4 -> [0,2]
+[...,-1, 2, 5, 6...], 4 -> [0,2]
+[1...9999], 4
+[1,2,9999], 4
+[1,1,2,2], 4
+[], 0
+[1,3,2,2], 4
+
+3. Brute
+    - 每個東西兩兩相加，如果是 target 就得到答案。
+
+---
+
+Allen
+
+3. Complexity
+Time: O(n^2)
+Space: O(1)
+ 
+5. Walk Through
+