From 6770fe8b150b7feaa5e79cf62fec4d977458d63c Mon Sep 17 00:00:00 2001
From: pezy-pc <urbancpz@gmail.com>
Date: Wed, 3 Dec 2014 08:48:46 +0800
Subject: [PATCH] added 50. Pascal's Triangle II

---
 50. Pascal's Triangle II/README.md  | 21 +++++++++++++++++++++
 50. Pascal's Triangle II/main.cc    | 11 +++++++++++
 50. Pascal's Triangle II/solution.h | 14 ++++++++++++++
 3 files changed, 46 insertions(+)
 create mode 100644 50. Pascal's Triangle II/README.md
 create mode 100644 50. Pascal's Triangle II/main.cc
 create mode 100644 50. Pascal's Triangle II/solution.h

diff --git a/50. Pascal's Triangle II/README.md b/50. Pascal's Triangle II/README.md
new file mode 100644
index 0000000..a7ca485
--- /dev/null
+++ b/50. Pascal's Triangle II/README.md	
@@ -0,0 +1,21 @@
+基础题，不多说，思路和 [32. Pascal's Triangle](32. Pascal's Triangle) 完全一致。
+
+-----
+
+重点总结一下杨辉三角的本质，我们提到杨辉三角，不要老想起那个正三角形的样子，那个样子只是让你更加形象的感受杨辉三角透露出来的数学美感，但在计算机的世界里，那东西就是格式拼凑的结果而已。
+
+我们应该想起的本质，其实应该是**一根皮筋**。如下图所示：
+
+```cpp
+|1| ------> drag
+
+|1|2|1| ------> drag
+
+|1|3|3|1| ------> drag
+
+|1|4|6|4|1| ------> drag
+```
+
+这样看起来，有没有点皮筋的感觉？你拽它，越拽越长，而中间受到的力，越来越大，使劲拽，会有一种要崩的感觉。上面图里，我最大拽到了6，再使劲，那个值会越来越大。
+
+所以杨辉三角，不要被什么三角迷惑，拉拉手边的皮筋，规律就在里面。
diff --git a/50. Pascal's Triangle II/main.cc b/50. Pascal's Triangle II/main.cc
new file mode 100644
index 0000000..85dc90b
--- /dev/null
+++ b/50. Pascal's Triangle II/main.cc	
@@ -0,0 +1,11 @@
+#include "solution.h"
+#include <iostream>
+
+int main()
+{
+    Solution s;
+    for (auto i : s.getRow(4))
+        std::cout << i << " ";
+    
+    return 0;
+}
diff --git a/50. Pascal's Triangle II/solution.h b/50. Pascal's Triangle II/solution.h
new file mode 100644
index 0000000..e6d7444
--- /dev/null
+++ b/50. Pascal's Triangle II/solution.h	
@@ -0,0 +1,14 @@
+#include <vector>
+using std::vector; 
+
+class Solution {
+public:
+    vector<int> getRow(int rowIndex) {
+        vector<int> vec(rowIndex+1, 0);
+        vec[0] = 1;
+        for (int i=0; i<=rowIndex; ++i)
+            for (int j=i; j>0; --j)
+                vec[j] += vec[j-1];
+        return vec;
+    }
+};