---
title: 'LeetCode 118. Pascals Triangle'
disqus: hackmd
---

# LeetCode 118. Pascal's Triangle

## Description

Given an integer numRows, return the first numRows of Pascal's triangle.

In Pascal's triangle, each number is the sum of the two numbers directly above it as shown:

## Example

Input: numRows = 5
Output: [[1],[1,1],[1,2,1],[1,3,3,1],[1,4,6,4,1]]

## Constraints

1 <= numRows <= 30

## Answer

此題主要是考雙重指標的操作，雙重指標相當於二維矩陣，頭尾先給值，外層for跑行，內層for跑列，第2列開始要計算，抓前一行的該列和前一列做疊加。

//2021_11_21
int** generate(int numRows, int* returnSize, int** returnColumnSizes) {
    int **ans = (int**)malloc(sizeof(int*)*numRows);
    *returnColumnSizes = (int*)malloc(sizeof(int)*numRows);
    *returnSize = 0;
    for(int i = 0; i < numRows; i++){
        (*returnColumnSizes)[*returnSize] = i + 1;
        ans[*returnSize] = (int*)malloc(sizeof(int)*(i + 1));
        ans[*returnSize][0] = 1;
        ans[*returnSize][i] = 1;
        if(i > 1){
            for(int j = 1; j < i; j++){
                ans[*returnSize][j] = ans[*returnSize - 1][j - 1] + ans[*returnSize - 1][j];
            }
        }
        (*returnSize)++;
    }
    return ans;
}

## Link
https://leetcode.com/problems/pascals-triangle/
###### tags: `Leetcode`