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 <list>
#include <vector>
#include <cstdlib>
#include <iterator>

//?????????
struct daruma {
	std::list<int> block;
	int size;
};

class DarumaOtosi {
public:
	DarumaOtosi(daruma d) {
		darumalist.resize(d.size-3);
		darumalist[d.size - 4].push_back(d);
	}
	//???????????????????????????
	int Hunmer(daruma d) {
		//?????????????????????
		if (d.size != d.block.size()) {
			//??????????????????????????´??°
			d.size = d.block.size();
			//????????\????????????????????????????????????
			if (d.size == 0 || d.size == 1) return d.size;
			//?????????????????????????????¨?????£?????£???
			if (d.size >= 4) {
				int tmp = CheckDaruma(d);
				if (tmp != 0) return tmp;
				darumalist[d.size - 4].push_back(d);
			}
		}

		for (auto itr = d.block.begin(); itr != std::prev(d.block.end()); itr++) {
			if (abs(*itr - *(std::next(itr))) <= 1) {
				const int tmp1 = *itr; const int tmp2 = *(std::next(itr));
				//????????????
				itr = d.block.erase(itr, std::next(itr, 2));
				//???????????£??????
				int size = Hunmer(d);
				//????????????
				itr = d.block.insert(itr, tmp2);
				itr = d.block.insert(itr, tmp1);
				//???????????´??°
				if (d.size > size) {
					d.size = size;
					//????????\???????????????????????£?????????
					if (d.size == 0 || d.size == 1) break;
				}
			}
		}

		if(d.block.size() >= 4) darumalist[d.block.size() - 4].back().size = d.size;
		return d.size;
	}

private:
	std::vector<std::vector<daruma>> darumalist;

	//????????????????????????
	void CollectDaruma(daruma d) {
		darumalist[d.size].push_back(d);
	}

	//???????????¨??????????????????????????§??????
	int CheckDaruma(daruma d) {
		int n = d.size;
		for (int i = 0; i < darumalist[n-4].size(); i++) {
			if (d.block == darumalist[n-4][i].block) return darumalist[n-4][i].size;
		}
		return 0;
	}
};

int main() {
	int n = 1;
	std::vector<daruma> daruma_original;

	//??\???
	for (int m;;) {
		daruma daruma;
		std::cin >> n;
		if (n == 0) break;
		for (int i = 0; i < n; i++) {
			std::cin >> m;
			daruma.block.push_back(m);
		}
		daruma.size = daruma.block.size();
		daruma_original.push_back(daruma);
	}

	//???????????????
	for (auto x : daruma_original) {
		DarumaOtosi darumaotosi(x);
		std::cout << x.size - darumaotosi.Hunmer(x) << std::endl;
	}

	getchar(); getchar();

	return 0;
}

C++: #include <bits/stdc++.h>
using namespace std;
#define FOR(i,a,b) for(int i=(a);i<(b);++i)
#define rep(i,n)   FOR(i,0,n)
#define pb emplace_back
typedef long long ll;
typedef pair<int,int> pint;

int dp[301][301];
int w[301];
int main(){
    int n;
    while(cin>>n,n){
        rep(i,n)cin>>w[i];
        memset(dp,0,sizeof(dp));
        FOR(d,2,n+1){
            rep(i,n-d+1){
                int l=i,r=i+d-1;
                if(abs(w[l]-w[r])<2&&dp[l+1][r-1]==d-2) dp[l][r]=dp[l+1][r-1]+2;
                else{
                    int mx=0;
                    FOR(j,l,r) mx=max(mx,dp[l][j]+dp[j+1][r]);
                    dp[l][r]=max(mx,dp[l][r]);
                }
            }
        }
        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 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 0;

	int ans = 0;
	for(int i = left+1; i <= right-2; i++){
		ans = max(ans,recursive(left,i)+recursive(i+1,right));
	}
	return dp[left][right] = ans;
}

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[151];
	}

	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] = -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;
}