title: Count Ways Build Street Given Constraints
signature: class Solution {
  
      public int CountWaysBuildStreetGivenConstraints(int n) {
test_code: using System;
  using System.Numerics;
  using System.Diagnostics;
  using System.Collections.Generic;
  using System.Linq;
  using System.Text;
  using System.Security.Cryptography;
  using System.Web.UI;
  using System.Web.Script.Serialization;
  
  // SOLUTION CODE
  // ============================================
  PLACEHOLDER_CODE_BODY
  
  // TESTING CODE 
  // ============================================
  namespace EvaluatePrediction {
      class TestRunner {
          public bool ValidateSolution(int actual, int expected){
              return new JavaScriptSerializer().Serialize(actual) == new JavaScriptSerializer().Serialize(expected);
          }
  
          public string driver(int n, int expected){
              try{
                PLACEHOLDER_CLS_NAME solution_cls = new PLACEHOLDER_CLS_NAME();
                int pred_result = solution_cls.PLACEHOLDER_FN_NAME(n); 
                if (ValidateSolution(
                      pred_result,
                      expected)){
                  return "PASSED";
                }
                return "FAILED";
              } 
              catch (Exception exception_obj)
              {
                return exception_obj.GetType().FullName;
              }
          }
          static void Main(string[] args) {
              TestRunner runner = new TestRunner();
              String result;
              result = runner.driver(
                  20, 
                  54608393
              );
              Console.WriteLine(string.Format(
                  "TEST-0...{0}",
                  result)
              );result = runner.driver(
                  1, 
                  3
              );
              Console.WriteLine(string.Format(
                  "TEST-1...{0}",
                  result)
              );
          }
      }
  }
  
source_py: def count_ways_build_street_given_constraints(n):
      dp = [([0] * (n + 1)) for i in range(2)]
      dp[0][1] = 1
      dp[1][1] = 2
      for i in range(2, (n + 1)):
          dp[0][i] = (dp[0][(i - 1)] + dp[1][(i - 1)])
          dp[1][i] = ((dp[0][(i - 1)] * 2) + dp[1][(i - 1)])
      return (dp[0][n] + dp[1][n])
source_cpp: long count_ways_build_street_given_constraints(int n) {
    long dp [ 2 ] [ n + 1 ];
    dp [ 0 ] [ 1 ] = 1;
    dp [ 1 ] [ 1 ] = 2;
    for ( int i = 2;
    i <= n;
    i ++ ) {
      dp [ 0 ] [ i ] = dp [ 0 ] [ i - 1 ] + dp [ 1 ] [ i - 1 ];
      dp [ 1 ] [ i ] = dp [ 0 ] [ i - 1 ] * 2 + dp [ 1 ] [ i - 1 ];
    }
    return dp [ 0 ] [ n ] + dp [ 1 ] [ n ];
  }