[70] 爬楼梯

/**
 * @param {number} n
 * @return {number}
 */
var climbStairs = function (n) {
  let dp = [];
  dp[0] = 0;
  dp[1] = 1;
  dp[2] = 2;
  for (let i = 3; i <= n; i++) {
    dp[i] = dp[i - 1] + dp[i - 2]
  }
  return dp[n]
};