Question:

Given a non-negative index k where k ≤ 33, return the k index row of the Pascal’s triangle.

Note that the row index starts from 0.

119. Pascal's Triangle II - 图1
In Pascal’s triangle, each number is the sum of the two numbers directly above it.

Example:

  1. Input: 3
  2. Output: [1,3,3,1]

Solution:

  1. /**
  2.  * @param {number} rowIndex
  3.  * @return {number[]}
  4.  */
  5. var getRow = function(rowIndex) {
  6.     let result=[];
  7.     for(let i=0; i<rowIndex+1; i++){
  8.         let item = [1]; //第一个元素
  9.         if(i===1){
  10.             item.push(1); //第二行
  11.         }
  12.         if(i>1){
  13.           //循环上一个数组
  14.           let arr = result[i-1];
  15.           let sum;
  16.           for(let j=0 ; j<arr.length-1; j++){
  17.               sum = (arr[j]-0)+(arr[j+1]-0);
  18.               item.push(sum);
  19.           }
  20.           item.push(1);//最后一个元素
  21.         }
  22.         result.push(item);
  23.     }
  24.     return result[rowIndex];
  25. };

Runtime: 52 ms, faster than 89.39% of JavaScript online submissions for Pascal’s Triangle II.