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[LeetCode 118] Pascals Triangle

Problem

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 1:

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

Example 2:

Input: numRows = 1
Output: [[1]]

Constraints:

- 1 <= numRows <= 30

TypeScript

function generate(numRows: number): number[][] {
    let res: number[][] = [];
    
    const build = (num: number, parent: number[]): void => {
        if(num === numRows + 1) {
            return;
        }
        
        let temp: number[] = []
        
        for(let i = 0; i < num; i++){
            if(i === 0 || i === num - 1){
                temp.push(1)
            } else {
                temp.push(parent[i - 1] + parent[i]);    
            }
        }
        
        res.push(temp)
        build(num + 1, temp)
    }
    
    build(1, [])
    return res;
};

Reference