Go: package main

import (
	"bufio"
	"fmt"
	"io"
	"os"
	"strconv"
)

const (
	initialBufSize = 10000000
	maxBufSize     = 100000000
)

var sc *bufio.Scanner

func initScanner(r io.Reader) *bufio.Scanner {
	buf := make([]byte, initialBufSize)

	sc := bufio.NewScanner(r)
	sc.Buffer(buf, maxBufSize)
	sc.Split(bufio.ScanWords) // bufio.ScanLines
	return sc
}

func main() {
	sc = initScanner(os.Stdin)
	resolve()
}

func nextInt(sc *bufio.Scanner) int {
	sc.Scan()
	a, _ := strconv.Atoi(sc.Text())
	return int(a)
}
func nextString(sc *bufio.Scanner) string {
	sc.Scan()
	return sc.Text()
}

func nextIntSlice(sc *bufio.Scanner, n int) (a []int) {
	a = make([]int, n)
	for i := 0; i < n; i++ {
		a[i] = nextInt(sc)
	}
	return a
}

var dp [][]int

func initDP(n int) {
	dp = make([][]int, n+1)
	for i := 0; i < len(dp); i++ {
		dp[i] = make([]int, n+1)
		for j := 0; j < len(dp[0]); j++ {
			dp[i][j] = -1
		}
	}
}

func resolve() {
	ans := []int{}
	for true {
		n := nextInt(sc)
		if n == 0 {
			break
		}
		as := nextIntSlice(sc, n)
		initDP(n)
		_rec(as, n, 0, n)
		ans = append(ans, dp[0][n])
	}
	for _, v := range ans {
		fmt.Println(v)
	}
	return
}

func _rec(as []int, n, l, r int) int {
	if dp[l][r] > -1 {
		return dp[l][r]
	}
	if r-l == 1 { // prevent to hit daruma
		dp[l][r] = 0
		return dp[l][r]
	}
	if r-l == 2 {
		if abs(as[l]-as[r-1]) <= 1 {
			dp[l][r] = 2
		} else {
			dp[l][r] = 0
		}
		return dp[l][r]
	}
	if abs(as[l]-as[r-1]) <= 1 {
		v := _rec(as, n, l+1, r-1)
		// if we can remove internal blocks
		if (r - 1 - (l + 1)) == v {
			dp[l][r] = v + 2
			return dp[l][r]
		} else {
			dp[l][r] = v
		}
	}
	for i := l + 1; i < r; i++ {
		v := _rec(as, n, l, i) + _rec(as, n, i, r)
		if dp[l][r] < v {
			dp[l][r] = v
		}
	}
	return dp[l][r]
}

func abs(v int) int {
	if v < 0 {
		return -v
	}
	return v
}

C++: #include "bits/stdc++.h"
using namespace std;

vector<int>as;
bool ok(int a,int b){
  return abs(as[a]-as[b])<=1;
}

int main() {
  while(1){
    
    int N;cin>>N;
    if(!N)break;
    as.resize(N);
    vector<vector<int>>dp(N+1,vector<int>(N+1,-100000));
    for(int i=0;i<N;++i){
      int a;cin>>a;as[i]=a;
    }
    for(int i=0;i<=N;++i){
      dp[i][i]=0;
    }
    for(int t=2;t<=N;++t){
      for(int l=0;l<=N-t;++l){
	const int r=l+t;
	dp[l][r]=max(dp[l+1][r],dp[l][r-1]);
	if(ok(l,l+1))dp[l][r]=max(dp[l+2][r]+2,dp[l][r]);
	if(ok(r-2,r-1))dp[l][r]=max(dp[l][r-2]+2,dp[l][r]);
	if(ok(l,r-1)){
	  if(dp[l+1][r-1]==(r-l-2)){
	    dp[l][r]=max(dp[l+1][r-1]+2,dp[l][r]);
	  }
	}
	for(int m=l+1;m<=r-1;++m){
	  dp[l][r]=max(dp[l][m]+dp[m][r],dp[l][r]);
	}
      } 
    }

    int ans=dp[0][N];
    ans=max(0,ans);
    cout<<ans<<endl;
  }
  return 0;
}

C++: #include <stdio.h>
#include <cmath>
#include <algorithm>
#include <stack>
#include <queue>
#include <vector>
typedef long long int ll;
#define BIG_NUM 2000000000
#define MOD 1000000007
using namespace std;

int main(){

	int N,data[301];
	bool** table = new bool*[301]; //table[left][right] = left???????§?????????????2*right??????????????¨?¶??????§??????????????????
	int** maximum = new int*[301]; //?????????????????????????????§?¶????????????°
	for(int i = 0; i <= 300; i++){
		table[i] = new bool[151];
		maximum[i] = new int[301];
	}

	bool FLG;

	while(true){
		scanf("%d",&N);
		if(N == 0)break;

		if(N <= 1){
			printf("0\n");
			continue;
		}

		//?¶??????????????????????????????????
		for(int i = 1; i <= N; i++){
			for(int k = 0; k <= N/2; k++)table[i][k] = false;
			for(int k = 1; k <= N; k++)maximum[i][k] = 0;
		}

		for(int i = 1; i <= N; i++)scanf("%d",&data[i]);

		//????????????2???????¨?
		for(int i = 1; i <= N-1; i++){
			if(abs(data[i+1]-data[i]) <= 1){
				table[i][1] = true;
				maximum[i][i+1] = 2;
			}
		}

		//?¶??????????????????????????¨????
		for(int length = 4; length <= N; length += 2){ //??????????????????
			for(int left = 1; left+length -1 <= N; left++){ //??????????????????
				FLG = false;

				if(table[left+1][(length-2)/2] == true && abs(data[left] - data[left+length-1]) <= 1)FLG = true;//??????????????£?????????length-2??????????¶????????????????????????¨??????+length-1?????´???????????????????¶?????????´???

				if(!FLG){
					for(int i = 2; i <= length-2; i += 2){
						if(table[left][i/2] == true && table[left+i][(length-i)/2] == true){
							FLG = true;
							break;
						}
					}
				}
				if(FLG){
					table[left][length/2] = true;
					maximum[left][left+length-1] = length; //????¨?????????§??????OK????????§?????¶????????§???????¨????
				}else{
					//maximum[left][left+length-1]?????´??°????????°????????????
					for(int div = 0; left+div <= left+length-2;div++){ //????´¢?§????????????????
						for(int i = 2; left+div+i-1 <= left+length-1; i+= 2){ //????´¢?§?????????????????????´?????????????????§????????¢?????????
							maximum[left][left+length-1] = max(maximum[left][left+length-1],maximum[left+div][left+div+i-1]+maximum[left+div+i][left+length-1]);
						}
					}
					//printf("maximum[%d][%d]:%d\n",left,left+length-1,maximum[left][left+length-1]);
				}
			}
		}

		if(N%2 == 0)printf("%d\n",maximum[1][N]);
		else{
			printf("%d\n",max(maximum[1][N-1],maximum[2][N]));
		}

	}

	return 0;
}

C++:  #include<bits/stdc++.h>
 using namespace std;
#define INF 1000000000
#define REP(i,n) for(int (i)=0;(i)<(int)(n);(i)++)
typedef long long LL;
int N;
bool ok[1001][1001];
int dp[1001][1001];
int ans[1001];
int main(){
    while(cin>>N,N){
       vector<int>v(N);
       REP(i,N)cin>>v[i];
       REP(i,1001)REP(j,1001){ok[i][j]=false;dp[i][j]=0;}
       //ok????????????
       /*REP(i,N){
           for(int j=i+1;j<N;j++){
               if(j-i==1&&abs(v[i]-v[j])<=1){ok[i][j]=true;dp[i][j]=2;continue;}
               if(j-i==2){ok[i][j]=false;dp[i][j]=0;continue;}
               for(int k=i+1;k+1<j;k++){
                   if(abs(v[i]-v[j])>1)continue;
                   if(ok[i][k]==false)continue;
                   if(ok[k+1][j]==false)continue;
                   ok[i][j]=true;
                   dp[i][j]=j-i+1;
               }
           }
       }*/
       for(int k=1;k<=N-1;k++){
          REP(i,N){
              if(i+k>=N)continue;
              if(k==1&&abs(v[i]-v[i+1])<=1){ok[i][i+1]=true;dp[i][i+1]=2;continue;}
              if(k==1)continue;
              if(k==2){ok[i][i+2]=false;dp[i][i+2]=0;continue;}
              if(abs(v[i]-v[i+k])<=1&&ok[i+1][i+k-1]==true){ok[i][i+k]=true;dp[i][i+k]=k+1;}
              for(int j=1;j<=k;j++){
                  if(ok[i][i+j]&&ok[i+j+1][i+k]){ok[i][i+k]=true;dp[i][i+k]=k+1;}
                  /*if(abs(v[i]-v[i+j]>1))continue;
                  if(ok[i][i+j-1]==false)continue;
                  if(ok[i+j+1][i+k]==false)continue;
                  ok[i][i+k]=true;
                  dp[i][i+k]=k+1;*/
              }
          }
       }
       REP(i,1001){
           ans[i]=0;
       }
       for(int i=1;i<N;i++){
           ans[i]=max(ans[i],ans[i-1]);
           ans[i]=max(ans[i],dp[0][i]);
           for(int j=0;j<i;j++){
               ans[i]=max(ans[i],ans[j]+dp[j+1][i]);
           }
       }
       //REP(i,N){REP(j,N)cout<<dp[i][j]<<" ";cout<<endl;}
       //REP(i,N)cout<<ans[i]<<endl;
       cout<<ans[N-1]<<endl;
    }
    return 0;
}