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OJ notes/pages/Leetcode Pascal's-Triangle-II.md

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+# Leetcode Pascal's-Triangle-II
+
+2022-09-02 14:54
+
+> ##### Algorithms:
+> #algorithm #recursion
+> ##### Data structures:
+> #DS #array
+> ##### Difficulty:
+> #coding_problem #difficulty-easy
+> ##### Additional tags:
+> #leetcode 
+> ##### Revisions:
+> N/A
+
+##### Links:
+- [Link to problem](https://leetcode.com/problems/pascals-triangle-ii/)
+___
+### Problem
+
+Given an integer `rowIndex`, return the `rowIndexth` (**0-indexed**) row of the **Pascal's triangle**.
+
+In **Pascal's triangle**, each number is the sum of the two numbers directly above it as shown:
+
+![](https://upload.wikimedia.org/wikipedia/commons/0/0d/PascalTriangleAnimated2.gif)
+
+#### Examples
+
+**Example 1:**
+
+**Input:** rowIndex = 3
+**Output:** [1,3,3,1]
+
+**Example 2:**
+
+**Input:** rowIndex = 0
+**Output:** [1]
+
+**Example 3:**
+
+**Input:** rowIndex = 1
+**Output:** [1,1]
+
+#### Constraints
+
+- `0 <= rowIndex <= 33`
+
+### Thoughts
+
+> [!summary]
+> This is a #recursion problem.
+
+Because to get the nth row, we have to get the `n - 1` th
+row, we use recursion.
+
+### Solution
+
+```cpp
+class Solution {
+public:
+  vector<int> getRow(int rowIndex) {
+    // recursion
+
+    if (rowIndex == 0) {
+      return {1};
+    }
+
+    auto last = getRow(rowIndex - 1);
+
+    vector<int> ans;
+
+    ans.push_back(1);
+
+    for (int i = 1; i < rowIndex; i++) {
+      ans.push_back(last[i] + last[i - 1]);
+    }
+
+    ans.push_back(1);
+
+    return ans;
+  }
+};
+```