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 <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],ans;
	bool** table = new bool*[301];
	int** dp = new int*[301];
	for(int i = 0; i <= 300; i++){
		table[i] = new bool[151];
		dp[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 = 0; i <= 300; i++){
			for(int k = 0; k <= 150; k++)table[i][k] = false;
			for(int k = 0; k <= 300; k++){
				dp[i][k] = 0;
			}
		}

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

		for(int i = 1; i <= N-1; i++){
			if(abs(data[i+1]-data[i]) <= 1){
				table[i][1] = true;
				dp[i][i+1] = 2;
			}else{
				dp[i][i+2] = 0;
			}
		}

		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;

				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;
					dp[left][left+length-1] = length;
				}
			}
		}

		ans = 0;

		for(int length = 4; length <= N; length += 2){ //??????????????????
			for(int left = N-(length/2);left >= N-length+2; left--){ //????????¨???????????????
				dp[left][N] = max(dp[left+1][left+(length-2)-1],max(dp[left][left+(length-2)+1],dp[left+1][N])); //?????????????????????????????§????????????
			}
			for(int left = N-length+1; left >= 1; left--){ //?§????????????????
				if(dp[left][left+length-1] != 0){ //?§£????±??????£???????????????????????????
					ans = max(ans,dp[left][left+length-1]);
					continue;
				}
				for(int mid = left+1; mid <= left+length-3; mid++){
					dp[left][left+length-1] = max(dp[left][left+length-1],dp[left][mid]+dp[min(left+length-1,mid+1)][left+length-1]);
					ans = max(ans,dp[left][left+length-1]);
				}
			}
		}
		/*for(int i = 1; i <= N-1; i++){
			for(int k = i+1; k <= N; k++){
				printf("dp[%d][%d]:%d\n",i,k,dp[i][k]);
			}
		}*/
		printf("%d\n",ans);
	}

	return 0;
}

C++: #include<bits/stdc++.h>
using namespace std;
void solve(int n){
    int w[n];
    for(int i=0;i<n;i++)scanf("%d",&w[i]);
    vector<vector<int>> dp(n,vector<int>(n));
    for(int i=0;i<n-1;i++)dp[i][i+1]=(abs(w[i]-w[i+1])<=1)*2;
    for(int k=2;k<n;k++){
        for(int i=0;i<n-k;i++){
            int j=i+k;
            if(dp[i+1][j-1]==j-i-1 and abs(w[i]-w[j])<=1)dp[i][j]=j-i+1;
            else{
                for(int l=i;l<j;l++)dp[i][j]=max(dp[i][j],dp[i][l]+dp[l+1][j]);
            }
        }
    }
    printf("%d\n",dp[0][n-1]);
}
int main(){
    while(true){
        int n;scanf("%d",&n);
        if(!n)break;
        solve(n);
    }
    return 0;
}

C++: #include<bits/stdc++.h>
#define vi vector<int>
#define vvi vector<vector<int> >
template<typename Head, typename... Tail> auto vectors(Head x, Tail... tail) { auto inner = vectors(tail...); return vectors<decltype(inner)>(x, inner); }
using ll = long long;
using ld =long double;
#define int ll
#define INF 1e9
#define EPS 0.0000000001
#define rep(i,n) for(int i=0;i<n;i++)
#define loop(i,s,n) for(int i=s;i<n;i++)
#define all(in) in.begin(), in.end()
template<class T, class S> void cmin(T &a, const S &b) { if (a > b)a = b; }
template<class T, class S> void cmax(T &a, const S &b) { if (a < b)a = b; }
#define MAX 9999999
int dx[]={0,0,1,-1};
int dy[]={1,-1,0,0};
int W,H;
bool inrange(int x,int y){return (0<=x&&x<W)&&(0<=y&&y<H);}
using namespace std;
typedef pair<int, int> pii;
typedef pair<int,pii> piii;
#define MP make_pair
signed main(){
    int n;
    while(cin >> n,n){
        vector<vector<int>>dp(n,vector<int>(n,0));
        vector<int>array(n);
        rep(i,n) cin >> array[i];
        rep(k,n)rep(i,n-1){
            if(!k || i+k>n-1)continue;
            if(k == 1){
                if(abs(array[i]-array[i+1]) <= 1) dp[i][i+k] = 1;
            } else{
                if((abs(array[i]-array[i+k])<=1 && dp[i+1][i+k-1])){
                    cmax(dp[i][i+k],dp[i+1][i+k-1]+2);
                }
                for(int j = i+1; j<i+k;j++){
                    if(dp[i][j] && dp[j+1][i+k])cmax(dp[i][i+k],dp[i][j] + dp[j+1][i+k]);
                }
            }
        }
        int ans = 0;
        for (int s = 0;s < n;s++){
            int temp = 0;
            for(int i = s; i<n;i++){
                for(int j = n-1; j >= 0;--j){
                    if(dp[i][j]){
                        temp += j-i+1;
                        i = j;
                    }
                }
                cmax(ans, temp);
            }
        }
        cout << ans << endl;
    }
}

C++: #include<iostream>
#include<vector>
#include<algorithm>
#include<cmath>
using namespace std;
int n, a[1000], dp[1000][1000];
int main() {
	while (true) {
		cin >> n; if (n == 0)break; for (int i = 0; i < 1000; i++) { for (int j = 0; j < 1000; j++)dp[i][j] = 0; }
		for (int i = 0; i < n; i++)cin >> a[i];
		for (int i = 0; i < n - 1; i++) { if (abs(a[i] - a[i + 1]) <= 1) { dp[i][i + 1] = 2; } }
		for (int i = 1; i <= n; i++) {
			for (int j = 0; j <= n; j++) {
				int a1 = j, a3 = i + j; if (a3 >= n)continue;
				for (int k = a1 + 1; k <= a3; k++) {
					int a2 = k;
					dp[a1][a3] = max(dp[a1][a3], dp[a1][a2 - 1] + dp[a2][a3]);
				}
				if (dp[a1][a3] >= 1 && a1 > 0 && a3 < n - 1 && abs(a[a1 - 1] - a[a3 + 1]) <= 1) {
					dp[a1 - 1][a3 + 1] = i + 3;
				}
			}
		}
		cout << dp[0][n - 1] << endl;
	}
	return 0;
}