Pascal-Triangle

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 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

Solutions

Python3

class Solution:
    def generate(self, numRows: int) -> List[List[int]]:
        res = []
        for i in range(numRows):
            t = [1 if j == 0 or j == i else 0 for j in range(i + 1)]
            for j in range(1, i):
                t[j] = res[i - 1][j - 1] + res[i - 1][j]
            res.append(t)
        return res

Java

class Solution {
    public List<List<Integer>> generate(int numRows) {
        List<List<Integer>> res = new ArrayList<>();
        for (int i = 0; i < numRows; ++i) {
            List<Integer> t = new ArrayList<>();
            for (int j = 0; j < i + 1; ++j) {
                boolean firstOrLast = j == 0 || j == i;
                t.add(firstOrLast ? 1 : 0);
            }
            for (int j = 1; j < i; ++j) {
                int val = res.get(i - 1).get(j - 1) + res.get(i - 1).get(j);
                t.set(j, val);
            }
            res.add(t);
        }
        return res;
    }
}

TypeScript

function generate(numRows: number): number[][] {
    if (numRows == 0) return [];
    let ans = [[1]];
    for (let i = 1; i < numRows; ++i) {
        ans.push(new Array(i + 1).fill(1));
        let half = i >> 1;
        for (let j = 1; j <= half; ++j) {
            let cur = ans[i - 1][j - 1] + ans[i - 1][j];
            ans[i][j] = cur;
            ans[i][i - j] = cur;
        }
    }
    return ans;
}

C++

class Solution {
public:
    vector<vector<int>> generate(int numRows) {
        vector<vector<int>> res;
        for (int i = 0; i < numRows; ++i) {
            vector<int> t(i + 1);
            t[0] = 1;
            t[i] = 1;
            for (int j = 1; j < i; ++j) {
                t[j] = res[i - 1][j - 1] + res[i - 1][j];
            }
            res.push_back(t);
        }
        return res;
    }
};

Go

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

JavaScript

const generate = function (numRows) {
    let arr = [];
    for (let i = 0; i < numRows; i++) {
        let row = [];
        row[0] = 1;
        row[i] = 1;
        for (let j = 1; j < row.length - 1; j++) {
            row[j] = arr[i - 1][j - 1] + arr[i - 1][j];
        }
        arr.push(row);
    }
    return arr;
};

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