118. 杨辉三角

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