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>
#define rep(i,s,e) for(int i = s; i < e; i++)
using namespace std;


int main()
{
    int n;
    while(scanf("%d", &n) && n != 0)
    {
        int daruma[n];

        rep(i,0,n)
            cin >> daruma[i];

        bool interval[n][n];
        memset(interval, 0, sizeof(interval));

        rep(i,0,n-1)
            if(abs(daruma[i]-daruma[i+1]) <= 1)
                interval[i][i+1] = true; 
            
        rep(i,0,n)
            rep(j,0,n-i)
                if((interval[j+1][j+i-1] && abs(daruma[j]-daruma[j+i]) <= 1))  
                    interval[j][j+i] = true;
                else
                    rep(k,j,j+i)
                        if(interval[j][k] && interval[k+1][j+i])
                            interval[j][j+i] = true;

        int dp[n][n];
        memset(dp,0,sizeof(dp));

        rep(i,0,n-1)
            rep(j,i+1,n)
                if(interval[i][j])
                    dp[i][j] = j-i+1;

        rep(j,0,n)
            rep(k,0,j)
               dp[0][j] = max(dp[0][j], dp[0][k] + dp[k+1][j]);

        cout << dp[0][n-1] << endl;
    }
    return 0;
}

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

int main(){
  int i,j,k;
  int n;
  while(1){
  cin>>n;
    if(n==0) {
      return 0;
    }
  int w[n+1];
  int dp[n+1][n+1];
  for(i=1;i<=n;i++) cin>>w[i];
  for(k=0;k<=n-1;k++){
    for(i=1;i<=n-k;i++){
      if(k==0) dp[i][i+k]=0;
      else if(k==1) {
        if(abs(w[i]-w[i+1])<=1) dp[i][i+1]=2;
        else dp[i][i+1]=0;
      }
      else {
        if(abs(w[i]-w[i+k])<=1&&dp[i+1][i+k-1]==k-1) dp[i][i+k]=k+1;
        else dp[i][i+k]=0;
          for(j=i;j<=i+k-1;j++) dp[i][i+k]=max(dp[i][i+k],dp[i][j]+dp[j+1][i+k]);
      }
    }
  }
  // for (int i = 1; i < n; i++) {
  //   for (int j = i; j < n; j++) {
  //     // cout << "dp[" << i << "][" << j << "]" << "\t\t" <<  dp[i][j] << endl;
  //   }
  // }
  cout<<dp[1][n]<<endl;
  }
}

C++: #ifdef BUILT_LOCAL

#include "niklib.h"

#endif

#include <iostream>
#include <utility>
#include <vector>
#include <stack>
#include <queue>
#include <algorithm>
#include <string>
#include <cstdio>
#include <map>
#include <cmath>
#include <set>
#include <list>

using namespace std;

typedef long long ll;
typedef unsigned long long ull;
typedef __int128 lll;
constexpr ll mod = 1000000007;

int dp[300][301];

int main() {
    while (true) {
        int n, *w;
        cin >> n;
        if (n == 0) return 0;
        w = new int[n];
        for (int i = 0; i < n; i++) {
            cin >> w[i];
        }
        for (auto &e:dp)for (auto &f:e)f = 0;
        for (int i = 2; i <= n; i++) {
            for (int j = 0; j + i <= n; j++) {
                if (dp[j + 1][j + i - 1] == i - 2 && abs(w[j] - w[j + i - 1]) < 2) {
                    dp[j][j + i] = dp[j + 1][j + i - 1] + 2;
                }
                for(int k = 0;k <= i;k++) {
                    dp[j][j+i] = max(dp[j][j+i],dp[j][j+k]+dp[j+k][j+i]);
                }
            }
        }
        cout << dp[0][n] << endl;
    }

}

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[min(left+length-1,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;
}