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 <cstdio>
#include <iostream>
#include <algorithm>
#include <vector>

#define DEBUG

#ifdef DEBUG

#define printd printf

#else

#define printd(...)

#endif

std::vector<int> weights(300, 0);
std::vector<std::vector<uint>> dp(302, std::vector<uint>(302, 0));

int solve(int num_daruma)
{
    for (uint i = 0; i < num_daruma; i++)
    {
        std::cin >> weights[i];
    }

    for (uint i = 0; i <= num_daruma; i++)
    {
        std::fill(dp[i].begin(), dp[i].begin() + num_daruma + 1, 0);
    }

    for (uint width = 1; width <= num_daruma; width++)
    {
        for (uint l = 0; l <= num_daruma - width; l++)
        {
            auto r = l + width;

            if (width >= 2 && dp[l + 1][r - 1] == r - l - 2 && abs(weights[l] - weights[r - 1]) < 2)
            {
                dp[l][r] = std::max({dp[l][r], r - l});
                continue;
            }

            for (uint mid = l + 1; mid < r; mid++)
            {
                dp[l][r] = std::max({dp[l][r], dp[l][mid] + dp[mid][r]});
            }
        }
    }

    return dp[0][num_daruma];
}

int main()
{
    int num_daruma = -1;

    while (true)
    {
        std::cin >> num_daruma;
        if (num_daruma == 0)
        {
            break;
        }
        std::cout << solve(num_daruma) << std::endl;
    }

    return 0;
}

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 h = 0; h < 10; h++) {
			for (int i = 2; i <= n; i++) {
				for (int j = 0; j < n; j++) {
					int a1 = j, a2 = i + j - 1; if (a2 >= n)continue;
					if (dp[a1][a2] == 0)continue;
					if (a1 > 0 && a2 < n - 1 && abs(a[a1 - 1] - a[a2 + 1]) <= 1)dp[a1 - 1][a2 + 1] = i + 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]);
					}
				}
			}
		}
		cout << dp[0][n - 1] << endl;
	}
	return 0;
}

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;

bool** table;
int** dp;
int N;

int recursive(int left,int right){

	if(dp[left][right] != -1)return dp[left][right]; //?????¢???????????´???
	if((right-left+1)%2 == 1){ //??????????\???°?????´???
		return dp[left][right] = max(recursive(left,right-1),recursive(left+1,right));
	}
	if(table[left][(right-left+1)/2] == true)return dp[left][right] = right-left+1; //left???right?????¨????¶?????????´???
	if(right == left+1 && table[left][1] == false)return dp[left][right] = 0;

	for(int i = left+1; i <= right-2; i++){
		dp[left][right] = max(dp[left][right],recursive(left,i)+recursive(i+1,right));
	}
	return dp[left][right];
}

int main(){

	int data[301];
	table = new bool*[301]; //table[left][right] = left???????§?????????????2*right??????????????¨?¶??????§??????????????????
	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 <= N; i++){
			for(int k = 0; k <= N/2; k++)table[i][k] = false;
			for(int k = 0; k <= N; k++){
				if(i == k)dp[i][k] = 0;
				else{
					dp[i][k] = -1;
				}
			}
		}

		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;

		}

		//?¶??????????????????????????¨????
		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;
				}
			}
		}

		printf("%d\n",recursive(1,N));
	}

	return 0;
}