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

#define REP(i, start, count) for (int i = (start); i < (int)(count); ++i)
#define rep(i, count) REP(i, 0, count)
#define ALLOF(c) (c).begin(), (c).end()

typedef long long ll;
typedef unsigned long long ull;

int n;
vector<int> w;
vector<vector<int>> dp;

// メモ化再帰（トップダウン）に書いていく
int rec(int l, int r) {
    int res = 0;
    // もう計算してる
    if (dp[l][r] != -1) return dp[l][r];

    // 範囲内に2個以上ない
    if (abs(r - l) <= 1) return 0;

    // lとrをはじき出せるパターン
    // - wの差が1
    // - 範囲内部 [l + 1, r - 1) が全て取り除ける(範囲r - l からスミの2個を除いたもの)
    if(abs(w[l] - w[r - 1]) <= 1 && rec(l + 1, r - 1) == r - l - 2) {
        res = r - l;
    }

    // 区間を細分化して解くパターン
    for(int mid = l + 1; mid <= r - 1; mid++) {
        res = max(res, rec(l, mid) + rec(mid, r));
    }

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

int main(void)
{
    int d;
    cin >> d;
    while (d != 0) {
        n = d;
        w.assign(n, 0);
        dp.assign(310, vector<int>(310, -1));
        
        rep(i, n)
        {
            cin >> w[i];
        }

        cout << rec(0, n) << endl;

        cin >> d;
    }
    return 0;
}

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

#define dump(x) cout << (x) << '\n'
#define Int int64_t
#define fi first
#define se second
#define all(x) (x).begin(), (x).end()

Int INF = 1e18;
int inf = 1e9;
Int mod = 1e9+7;

Int dp[301][301];

int main() {
    vector<Int> res;
    Int n;
    while (cin >> n and n) {
        vector<Int> a(n);
        for (Int i = 0; i < n; i++) {
            cin >> a[i];
        }
        for (Int i = 0; i <= 300; i++) {
            for (Int j = 0; j <= 300; j++) {
                dp[i][j] = 0;
            }
        }
        for (Int i = 0; i < n - 1; i++) {
            if (abs(a[i] - a[i + 1]) <= 1) {
                dp[i][i + 1] = 2;
            }
        }
        if (n == 1) {
            dump(0);
            return 0;
        }
        if (n == 2) {
            if (abs(a[0] - a[1]) <= 1) {
                dump(2);
            }
            else {
                dump(0);
            }
            return 0;
        }
        if (n == 3) {
            if (abs(a[0] - a[1]) <= 1 or abs(a[1] - a[2]) <= 1) {
                dump(2);
            }
            else {
                dump(0);
            }
            return 0;
        }
        for (Int i = 0; i + 3 < n; i++) {
            for (Int j = 0; j + i + 3 < n; j++) {
                if (dp[j + 1][j + i + 2] == i + 2) {
                    dp[j][j + i + 3] = i + 2;
                    if (abs(a[j] - a[j + i + 3]) <= 1) {
                        dp[j][j + i + 3] = max(dp[j][j + i + 3], dp[j + 1][j + i + 2] + 2);
                    }
                }
                for (Int k = j + 1; k < j + i + 3; k++) {
                    dp[j][j + i + 3] = max(dp[j][j + i + 3], dp[j][k] + dp[k + 1][j + i + 3]);
                }
            }
        }
        res.push_back(dp[0][n - 1]);
    }
    for (Int i = 0; i < (Int)res.size(); i++) {
        dump(res[i]);
    }
    return 0;
}

C++: #include<iostream>
using namespace std;

long long n_max = 300;

int main(){
    long long n;
    long long w[n_max + 1];
    long long i,j,d;
    long long dp[n_max + 1][n_max + 1];

    //input
    cin >> n;
    while(n > 0){
        for(i = 1; i <= n; i++){
            cin >> w[i];
        }

        //calc
        for(i = 1; i <= n-1; i++){
            dp[i][i+1] = 2*(abs(w[i]-w[i+1]) <= 1);
        }
        for(d = 3; d <= n-1; d += 2){
            for(i = 1; i <= n-d; i++){
                dp[i][i+d] = dp[i+1][i+d-1] + (dp[i+1][i+d-1] == d-1 ? 2*(abs(w[i]-w[i+d]) <= 1) : 0);
                for(j = i+1; j <= i+d-2; j += 2){
                    dp[i][i+d] = max(dp[i][i+d], dp[i][j] + dp[j+1][i+d]);
                }
            }
        }
        if(n % 2 == 1){
            dp[1][n] = max(dp[1][n-1], dp[2][n]);
        }

        //answer
        cout << dp[1][n] << endl;

        //input
        cin >> n;
    }
    return 0;
}