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 <iostream>
#include <vector>
#include <algorithm>
#include <cmath>

#define show(x) cerr << #x << " = " << x << endl
using namespace std;

template <typename T>
ostream& operator<<(ostream& os, const vector<T>& v)
{
    os << "sz:" << v.size() << "\n[";
    for (const auto& p : v) {
        os << p << ",";
    }
    os << "]\n";
    return os;
}

template <typename S, typename T>
ostream& operator<<(ostream& os, const pair<S, T>& p)
{
    os << "(" << p.first << "," << p.second
       << ")";
    return os;
}


int main()
{
    while (true) {
        int n;
        cin >> n;
        if (n == 0) {
            break;
        }
        vector<int> w(n);
        for (int i = 0; i < n; i++) {
            cin >> w[i];
        }

        vector<vector<bool>> ok(n, vector<bool>(n, false));  // [i,j]?????¨????????¨?????????
        for (int d = 1; d < n; d += 2) {
            for (int i = 0; i + d < n; i++) {
                if (d == 1) {
                    if (abs(w[i] - w[i + d]) <= 1) {
                        ok[i][i + d] = true;
                    }
                } else {
                    if (ok[i + 1][i + d - 1] and abs(w[i] - w[i + d]) <= 1) {
                        ok[i][i + d] = true;
                    } else {
                        for (int j = i + 1; j < i + d; j += 2) {
                            if (ok[i][j] and ok[j + 1][i + d]) {
                                ok[i][i + d] = true;
                                break;
                            }
                        }
                    }
                }
            }
        }
        vector<pair<int, int>> interval;
        for (int i = 0; i < n; i++) {
            for (int j = i + 1; j < n; j++) {
                if (ok[i][j]) {
                    interval.push_back(make_pair(i + 1, j + 1));
                }
            }
        }
        const int size = interval.size();
        vector<vector<int>> dp(size + 1, vector<int>(n + 1, 0));
        for (int i = 0; i < size; i++) {
            for (int j = 0; j <= n; j++) {
                dp[i + 1][j] = max(dp[i + 1][j], dp[i][j]);
                if (j < interval[i].first) {
                    dp[i + 1][interval[i].second] = max(dp[i + 1][interval[i].second], dp[i][j] + (interval[i].second - interval[i].first + 1));
                }
            }
        }

        int maxi = 0;
        for (int i = 0; i <= n; i++) {
            maxi = max(maxi, dp[size][i]);
        }
        cout << maxi << endl;
    }

    return 0;
}

C++: #include <bits/stdc++.h>

using namespace std;

#define INF 1001000100010001000
#define MOD 1000000007
#define EPS 1e-10
#define int long long
#define rep(i, N) for (int i = 0; i < N; i++)
#define Rep(i, N) for (int i = 1; i < N; i++)
#define For(i, a, b) for (int i = (a); i < (b); i++)
#define pb push_back
#define eb emplace_back
#define mp make_pair
#define i_i pair<int, int>
#define vi vector<int>
#define vvi vector<vi >
#define vb vector<bool>
#define vvb vector<vb >
#define vp vector< i_i >
#define all(a) (a).begin(), (a).end()
#define Int(x) int x; cin >> x;
#define int2(x, y) Int(x); Int(y);
#define int3(x, y, z) Int(x); int2(y, z);
#define fir first
#define sec second
#define ffir first.first
#define fsec first.second
#define sfir second.first
#define ssec second.second
#define Decimal fixed << setprecision(10)

//int dxy[5] = {0, 1, 0, -1, 0}; 

int n;
int data[300];
int dp[300][301]; // hankai
int score[300][301];

void make(int st, int en)
{
if (dp[st][en]) return;
dp[st][en] = 1;
if (0 <= st - 2 && abs(data[st-2] - data[st-1] ) < 2 ) {
make(st-2, en);
}
if (0 <= st - 1 && en < n && abs(data[st-1] - data[en]) < 2) {
make(st-1, en+1);
}
if (en + 1 < n && abs(data[en] - data[en+1]) < 2) {
make(st, en+2);
}
}

int solve(int st, int en)
{
if ( dp[st][en] ) return 0; 
if ( score[st][en] ) return score[st][en];
if (en - st < 2) return en - st;
int ret = en - st;
for (int i = st+2; i < en; i++) {
if (dp[st][i]) {
ret = min(solve(i-1, en), ret);
}
}
return score[st][en] = min(ret, 1+solve(st+1, en));
}

signed main() 
{ 
std::ios::sync_with_stdio(false); 
std::cin.tie(0); 

cin >> n;
while ( n ) {
memset(data, 0, sizeof(data))
memset(dp, 0, sizeof(dp));
rep(i, n) cin >> data[i];
rep(i, n-1) if ( abs(data[i] - data[i+1]) < 2 )
make(i, i+2);
cout << n - solve(0, n) <<endl;
cin >> n;
}

return 0; 
}

C++: // written by @kakira9618
// problem: http://icpc.iisf.or.jp/past-icpc/domestic2016/problems/all_ja.html#section_D

#include <iostream>
#include <vector>
#include <algorithm>
#include <string.h>

using namespace std;

int n;
vector<int> W;
int dp[301][301];

int dfs(int l, int r) {
    if (r - l <= 1) return dp[l][r] = 0;
    if (dp[l][r] != -1) return dp[l][r];
    int ans = 0;
    for(int i = l + 1; i < r - 1; i++) {
        ans = max(ans, dfs(l, i) + dfs(i, r));
    }
    if (abs(W[r - 1] - W[l]) <= 1) {
        if (dfs(l + 1, r - 1) == r - l - 2) {
            ans = max(ans, dfs(l + 1, r - 1) + 2);
        }
    }
    return dp[l][r] = ans;
}

int main() {
    while(cin >> n, n) {
        memset(dp, -1, sizeof(int) * 301 * 301);
        W.clear();
        W.resize(n);
        for(int i = 0; i < n; i++) {
            cin >> W[i];
        }
        cout << dfs(0, n) << endl;
    }
    return 0;
}