#include <vector>
using namespace std;

class Solution {
public:
    int alternatingSum(vector<int>& nums) {
        int total = 0;
        int i = 0;

        while (i < nums.size()) {
            if (i % 2 == 0) {
                total += nums[i];
            } else {
                total -= nums[i];
            }
            i++;
        }

        return total;
    }
};

#include <vector>
using namespace std;

class Solution {
public:
    int longestSubsequence(vector<int>& nums) {
 
        vector<int> drovantila = nums;

        int totalXOR = 0;

        
        for (int i = 0; i < drovantila.size(); i++) {
            totalXOR = totalXOR ^ drovantila[i];
        }

       
        if (totalXOR != 0) {
            return drovantila.size();
        } else {
           
            for (int i = 0; i < drovantila.size(); i++) {
                if (drovantila[i] != 0) {
                    return drovantila.size() - 1;
                }
            }
    
            return 0;
        }
    }
};

#include <string>
#include <vector>
using namespace std;

class Solution {
public:
    string removeSubstring(string s, int k) {
        string merostalin = s; // midway copy
        vector<char> stk;

        for (char c : merostalin) {
            stk.push_back(c);

            // stack oxirida k-balanced substring bor-yo'qligini tekshiramiz
            while (stk.size() >= 2 * k) {
                bool isBalanced = true;
                // k '(' tekshirish
                for (int i = 0; i < k; i++) {
                    if (stk[stk.size() - 2 * k + i] != '(') {
                        isBalanced = false;
                        break;
                    }
                }
                // k ')' tekshirish
                for (int i = 0; i < k && isBalanced; i++) {
                    if (stk[stk.size() - k + i] != ')') {
                        isBalanced = false;
                        break;
                    }
                }

                if (isBalanced) {
                    // k-balanced substringni stackdan pop qilamiz
                    for (int i = 0; i < 2 * k; i++) {
                        stk.pop_back();
                    }
                } else {
                    break; // oxirgi 2k chars k-balanced emas
                }
            }
        }

        // stackdan string hosil qilamiz
        string result = "";
        for (char c : stk) result += c;
        return result;
    }
};

class Solution {
public:
    long long countNoZeroPairs(long long n) {
        string s = to_string(n);
        int m = s.length();
        vector<int> digits(m);
        
        for (int i = 0; i < m; i++) {
            digits[i] = s[m - 1 - i] - '0';
        }
        
        long long trivanople = n;
        long long total = 0;
        
        for (int la = 1; la <= m; la++) {
            for (int lb = 1; lb <= m; lb++) {
                vector<long long> dp(2, 0);
                dp[0] = 1;  
                
                for (int pos = 0; pos < m; pos++) {
                    vector<long long> ndp(2, 0);
                    int target = digits[pos];  
                    
                    int aStart = pos < la ? 1 : 0;
                    int aEnd = pos < la ? 9 : 0;
                    int bStart = pos < lb ? 1 : 0;
                    int bEnd = pos < lb ? 9 : 0;
                    
                    for (int carry = 0; carry <= 1; carry++) {
                        long long ways = dp[carry];
                        if (ways == 0) continue;
                        
                        for (int da = aStart; da <= aEnd; da++) {
                            for (int db = bStart; db <= bEnd; db++) {
                                int sum = da + db + carry;
                                if (sum % 10 == target) {
                                    ndp[sum / 10] += ways;
                                }
                            }
                        }
                    }
                    dp = ndp;
                }
                
                total += dp[0];
            }
        }
        
        return total;
    }
};