118. 杨辉三角

/**
 * @param {number} numRows
 * @return {number[][]}
 */
var generate = function (numRows) {
  const result = [[1]]
  for (let i = 1; i < numRows; i++) {
    const rowResult = []
    for (let j = 0; j <= i; j++) {
      rowResult.push(j === 0 || j === i ? 1 : result[i - 1][j - 1] + result[i - 1][j])
    }
    result.push(rowResult)
  }
  return result
}