119 - Pascals Triangle II

119. Pascals Triangle II

Problem Statement

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:

 

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

 

Follow up: Could you optimize your algorithm to use only O(rowIndex) extra space?

Solutions

Rust

impl Solution {
    pub fn get_row(row_index: i32) -> Vec<i32> {
        // create a vector of 1s with length row_index + 1
        let mut row = vec![1; (row_index + 1) as usize];

        // loop through the vector, starting at 1
        for i in 1..row_index {
            // loop through the vector, starting at i + 1 and going backwards
            for j in (1..=i).rev() {
                // add the value at the current index to the value at the previous index
                row[j as usize] += row[(j - 1) as usize];
            }
        }

        row
    }
}

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