Code_snippets

Contents

• STL Usage
  • Priority Queues
  • Vectors

Count Number of Digits

def number_of_digits(x):
  count = 0
  while (x > 0):
    x = x // 10
    count+=1
  return count

count consecutive onse

def findMaxConsecutiveOnes(self, nums: List[int]) -> int:
        gcount = 0
        count = 0
        for x in nums:
            if x == 1:
                count +=1
                if count > gcount:
                    gcount = count
            elif x == 0:
                
                count = 0
            else:
                pass
        return gcount

561. Array Partition

make n pairs (a1, b1), (a2, b2), ..., (an, bn) such that the sum of min(ai, bi) for all i is maximized. Return the maximized sum.

int sum=0;
        sort(nums.begin(),nums.end());
        for(int i=0; i<nums.size(); i++){
            if(i%2=0){
                sum=sum+nums[i];
            }
        }
        return sum;

2553. Separate the Digits in an Array.eg 12,33==1,2,3,3

 vector<int> separateDigits(vector<int>& nums) {
        vector<int> answer;
        int n= nums.size();
        for(int i=0; i<n; i++){
            vector<int> temp;

            while(nums[i]>0){
                temp.push_back(nums[i]%10);
                nums[i]=nums[i]/10;
            }
            reverse(temp.begin(),temp.end());
            for(int x=0;x<temp.size();x++){
            answer.push_back(temp[x]);
            }
        }
        
        return answer;
    }

linklist traverse

  ListNode* temp = head;
        while(temp!= NULL){
            cout<<temp->val<<" ";
            temp= temp->next;
        }

array to integer number basic

int array_to_int(vector<int> v, int rflag) {
    int val = 0;
    
    if (rflag) {
        /* generating number in reverse*/
        for (int i = v.size() - 1; i >= 0; i--) {
            val = val *10 + v[i];
        }
        
    }else {
        /* generating number */
        for (int i = 0; i < v.size(); i++) {
            val = val *10 + v[i];
        }
    }
    return val;
}

int main() {
    std::cout << "Hello World!\n";
    int key = 1234;
    int tmp = key;
    int d = 0;
    int rkey = 0;
    
    while(tmp) {
        /*number to digits*/
        d =  tmp %10;
        tmp /= 10;
        
        /*digits to number*/
        rkey = rkey* 10 + d;
    }
    
    std::cout<< key <<" " << rkey<<std::endl;
    
    std::vector<int> v = {1, 2, 3, 4};
    
    std::cout<<"normal int : "<< array_to_int(v, 0) <<std::endl;
    std::cout<<"reverse int : "<< array_to_int(v, 1) <<std::endl;
    
}

character count using array

string data = "hello world how are you";
    vector<int> letter_count(26, 0);
    
    for(int i = 0; i < data.size(); i++) {
        if(data[i] == ' ') continue;
        int index = data[i] - 97;
    
        letter_count[index] = letter_count[index] + 1;   
    }
    
    for(int i = 0; i < data.size(); i++) {
       cout << letter_count[i] <<endl;
    }    

character count using hash_table

unordered_map<char, int> hash_map;
    for(int i = 0; i < data.size(); i++) {
        if(data[i] == ' ') continue;
        hash_map[data[i]]  = hash_map[data[i]] + 1; 
    }
    
    for (auto i: hash_map)
        cout << i.first << ":" << i.second <<endl;

create a compartor without function

struct
{
  bool operator()(int a, int b) const { return a < b; }
}customless;

sort(a.begin(), a.end(), customless);

search element in 2d array function

bool search(int arr[][3], int target){
      for(int i=0; i<3; i++){
        for(int j=0; j<3; j++){
            if(arr[i][j] == target)
            return 1;
        }
    }  
    return 0;
}

find sum of row in 2d array function

void sumrowwise(int arr[][3]){
      
      for(int i=0; i<3; i++){
        int sum=0;
        for(int j=0; j<3; j++){
            sum += arr[i][j];
        }
        cout<<sum<<" ";
    }
    cout<<endl;
}

find sum of col in 2d array function

void sumcolwise(int arr[][3]){
      
      for(int i=0; i<3; i++){
        int sum=0;
        for(int j=0; j<3; j++){
            sum += arr[j][i];
        }
        cout<<sum<<" ";
    }
    cout<<endl;
}

find max row sum and index of row in 2d array function

int largestrowsum(int arr[][3]){
     int max = INT_MIN;
     int rowindex=-1;
     for(int i=0; i<3; i++){
        int sum=0;
        for(int j=0; j<3; j++){
            sum += arr[i][j];
        }
        if(sum > max){
            max = sum;
            rowindex = i;
        }
    }
    cout<< "rowindex of row having maximum sum is" << rowindex<<endl;;
    return max;
}

find max col sum and index of col in 2d array function

int largestcolsum(int arr[][3]){
     int max = INT_MIN;
     int colindex=-1;
     for(int i=0; i<3; i++){
        int sum=0;
        for(int j=0; j<3; j++){
            sum += arr[j][i];
        }
        if(sum > max){
            max = sum;
            colindex = i;
        }
    }
    cout<< "rowindex of col having maximum sum is" << colindex<<endl;;
    return max;
}

STL usage

1. Priority Queue

priority_queue<T, Conatiner, Comparator> pq;

Params:
T	-	The type of the stored elements.  
Container	-	The type of the underlying container to use to store the elements.
Compare	-	A Compare type providing a strict weak ordering.
eg 
priority_queue<int, vector<int>, greater<int>> pq;

APIS:
front()
push_back()
pop_back()

2. Vectors

• Initializations:

vector<T> v1; => default initialization, v1 is empty;

vector<T> v2(v1); => v2 has copy of each element of v1;

vector<T> v2 = v1; => Equivalemnt of v2(v1);

vector<T> v3(n,val); => v3 has n elements with value val;

vector<T> v4(n); => v4 has n copies of vale-initialied object;

vector<T> v5{a,b,c}; => definig;

vector<T> v5 = {a,b,c}; => same as above;

Initializing 2d vectors

vector<vector<int>> table<ROWS_COUNT, vector<int>(COLS_COUNT)>;

vector<vector<int>> table<ROWS_COUNT, vector<int>(COLS_COUNT, val)>;