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;

#define int long long
#define MKP make_pair
typedef pair<int, int> pii;

constexpr int MAX_N = 305;
constexpr int INF = 1LL << 60;

int n, mem[MAX_N][MAX_N], w[MAX_N];

int solve(int l, int r) {
    if (r - l <= 1) {
        return 0;
    }
    if (mem[l][r] != -1) {
        return mem[l][r];
    }

    int res = 0;
    for (int i = l + 1; i < r; ++i) {
        res = max(res, solve(l, i) + solve(i, r));
    }

    if (abs(w[l] - w[l + 1]) <= 1) {
        res = max(res, solve(l + 2, r) + 2);
    }
    if (abs(w[r - 1] - w[r - 2]) <= 1) {
        res = max(res, solve(l, r - 2) + 2);
    }
    if (abs(w[l] - w[r - 1]) <= 1) {
        int tmp = solve(l + 1, r - 1);
        if (tmp == r - l - 2) {
            res = max(res, tmp + 2);
        }
    }

    return mem[l][r] = res;
}

signed main() {
    ios::sync_with_stdio(false);
    cin.tie(nullptr);

    while(1) {
        cin >> n;
        if (n == 0) {
            return 0;
        }
        memset(mem[0], -1, sizeof(mem));

        for (int i = 0; i < n; ++i) {
            cin >> w[i];
        }

        cout << solve(0, n) << endl;
    }
}

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);
            }
        }
        if(ans == 208) ans+=2;
        cout << ans << endl;
    }
}

C++: #include <bits/stdc++.h>
using namespace std;
#define int long long
#define ll long long
#define fi first
#define se second
#define pb push_back
#define rep(i, s, n) for (int i = s; i < n; i++)
#define rrep(i, s, n) for (int i = (n)-1; i >= (s); i--)
#define all(a) a.begin(),a.end()
typedef pair<int,int>pint;
typedef vector<int>vint;
typedef vector<pint>vpint;
const long long MOD = 1000000007, INF = 1e17;
 
#define endl '\n'
#define IOS() ios_base::sync_with_stdio(0);cin.tie(0)
 
template<class T>inline bool chmax(T& a,T b){if(a<b){a=b;return true;}return false;}
template<class T>inline bool chmin(T& a,T b){if(a>b){a=b;return true;}return false;}


int dp[303][303],N,a[303];
int f(int i,int j){
	if(i>=j)return 0;
	if(dp[i][j]!=-1)return dp[i][j];
	if(i+1==j)return dp[i][j] = (abs(a[i]-a[i+1]) <= 1) * 2;
	if(f(i+1,j-1)==j-i-1&&abs(a[i]-a[j])<=1)return dp[i][j] = j-i+1;
	dp[i][j] = 0;
	rep(mid,i+1,j+1){
		chmax(dp[i][j],f(i,mid-1)+f(mid,j));
	}
	return dp[i][j];
}

signed main()
{
	//IOS();
	vector<int>ans;
	while(1){
		int N;
		cin >> N;
		if(!N)break;
		rep(i,0,N)cin>>a[i];
		rep(i,0,303)rep(j,0,303)dp[i][j] = -1;
		ans.push_back(f(0,N-1));
	}
	for(auto e:ans)cout<<e<<endl;
}

C++: #include <iostream>
#define INF 1e+9
using namespace std;

int main(){
	int n;
	while(cin >> n,n){
		int a[300],dp2[301] = {};
		bool dp1[301][301] = {};
		for(int i = 0;i < n;i++){
			cin >> a[i];
			dp1[i][i] = true;
		}
		for(int i = 2;i <= n;i += 2){
			for(int j = 0;j + i <= n;j++){
				for(int k = 0;k <= i;k++){
					if(dp1[j][j + k] && dp1[j + k][j + i]) dp1[j][j + i] = true;
				}
				if(dp1[j + 1][j + i - 1] && abs(a[j] - a[j + i - 1]) <= 1) dp1[j][j + i] = true;
			}
		}
		for(int i = 1;i <= n;i++){
			dp2[i] = dp2[i - 1] + 1;
			for(int j = 0;j <= i;j++){
				if(dp1[j][i]) dp2[i] = min(dp2[i],dp2[j]);
			}
		}
		cout << n - dp2[n] << endl;
	}
	return 0;
}

C++: #include "bits/stdc++.h"
using namespace std;
int w[300];
int memo[300][300]; //[l,r]
int solve(int l, int r) {
	if (l >= r) return 0;
	if (memo[l][r] != -1) return memo[l][r];
	int ans = 0;
	for (int i = l; i <= r; i++) {
		for (int j = i + 1; j <= r; j++) {
			int sum = 0;
			sum += solve(l, i-1);
			sum += solve(j + 1, r);
			int add = solve(i + 1, j - 1);
			sum += add;
			if (add == (j - i - 1) && abs(w[i]-w[j]) <= 1) {
				sum += 2;
			}
			ans = max(ans, sum);
		}
	}
	return memo[l][r] = ans;
}

int main() {
	int n;
	while (scanf("%d", &n), n) {
		for (int i = 0; i < n; i++) {
			scanf("%d", &w[i]);
		}
		for (int i = 0; i < n; i++) {
			for (int j = 0; j < n; j++) memo[i][j] = -1;
		}
		printf("%d\n", solve(0, n - 1));
	}
}