Learning GoLang: Generate a Pascal Triangle

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]]

Generate a Pascal Triangle using GoLang

First declare a 2-dimension array with N rows, then fill each row, both ends are 1 and the internal value is equal to the sum of both numbers on its shoulder (Dynamic Programming Algorithm).

func generate(numRows int) [][]int {
    var res = make([][]int, numRows)
    for i := 0; i < numRows; i ++ {
        res[i] = make([]int, i + 1)
        res[i][0], res[i][i] = 1, 1
        for j := 1; j < i; j ++ {
            res[i][j] = res[i - 1][j] + res[i - 1][j - 1]
        }
    }
    return res
}

Another GoLang Implementation that appends row by row (beware that we need to deepcopy each row):

func generate(numRows int) [][]int {
    var res [][]int
    var cur []int    
    cur = append(cur, 1)
    for i := 0; i < numRows; i ++ {
        res = append(res, append([]int(nil), cur...))
        for j := i; j &gt; 0; j -- {
            cur[j] += cur[j - 1]
        }
        cur = append(cur, 1)
    }
    return res
}

Pascal Triangle Implementations:

• Teaching Kids Programming – Pascal Triangle Algorithms and Applications
• Coding Exercise – Pascal Triangle II – C++ and Python Solution
• How to Print Pascal Triangle in C++ (with Source Code)
• Compute the Nth Row of a Pascal's Triangle using Dynamic Programming Algorithm
• GoLang: Generate a Pascal Triangle

Reposted to Blog

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