C++ Articles

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Find number of subarrays with even sum in C++

sudhir sharma
sudhir sharma
Updated on 11-Mar-2026 449 Views

In this problem, we are given an array arr[] consisting of N elements. Our task is to find the subarray with even sum.Let’s take an example to understand the problem,Inputarr[] = {2, 1, 3, 4, 2, 5}Output28ExplanationThe subarrays are −{2}, {4}, {2}, {2, 4}, {2, 2}, {1, 3}, {1, 5}, {3, 5}, {4, 2}, {2, 1, 3}, {2, 1, 5}, {2, 3, 5}, {2, 4, 2}, {1, 3, 4}, {1, 3, 2}, {1, 4, 5}, {1, 2, 5}, {3, 4, 5}, {3, 2, 5}, {2, 1, 3, 4}, {2, 1, 3, 2}, {2, 3, 4, 5}, {2, 3, 2, 5}, {2, 4, 2, 5}, {1, 3, 4, 2}, {1, 4, 2, 5}, {3, 4, 2, 5}, {2, 1, 3, 4, 2}, {2, 1, 3, 4, 2, 5}Solution ApproachA simple solution to the problem is using the direct method which is by calculating all subarray and their sums. And the increase count for the subarray with even sum. And at last return count.Program to illustrate the working of our solution,Example#include using namespace std; int countEvenSumSubArray(int arr[], int n){    int evenSumCount = 0, sum = 0;    for (int i=0; i

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Find elements of an array which are divisible by N using STL in C++

Sunidhi Bansal
Sunidhi Bansal
Updated on 11-Mar-2026 314 Views

Given with an array and the task is to find the number which are divisible by N using standard template library in C++.To solve this problem we are using the function count_if() present in C++ standard template library.What is a count_if() function?Syntaxcount_if(LowerBound, UpperBound, function)Description − This function returns the number of elements in an array that satisfies the given condition. It takes three parameters.Lower Bound − It points to the first element of an array or any other sequence.Upper Bound − It points to the last element of an array or any other sequence.Function − It returns the Boolean value ...

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Count all elements in the array which appears at least K times after their first occurrence in C++

Ayush Gupta
Ayush Gupta
Updated on 11-Mar-2026 320 Views

In this tutorial, we will be discussing a program to find the number of elements in the array which appears at least K times after their first occurrence.For this we will be provided with an integer array and a value k. Our task is to count all the elements occurring k times among the elements after the element in consideration.Example#include #include using namespace std; //returning the count of elements int calc_count(int n, int arr[], int k){    int cnt, ans = 0;    //avoiding duplicates    map hash;    for (int i = 0; i < n; i++) ...

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Interval List Intersections in C++

Arnab Chakraborty
Arnab Chakraborty
Updated on 11-Mar-2026 379 Views

Suppose we have two lists of closed intervals, here each list of intervals is pairwise disjoint and in sorted order. We have ti find the intersection of these two interval lists.We know that the closed interval [a, b] is denoted as a A[i][1] or A[i][1] B[j][1] or B[j][1] B[j][1]:          j+=1       else:          i+=1    return result    def intersect(self,a,b):       if a[0]=b[0]:          return True       if b[0]=a[0]:          return True       return False ob = Solution() print(ob.intervalIntersection([[0,2],[5,10],[13,23],[24,25]],[[1,5],[8,12],[15,24],[25,27]]))Input[[0,2],[5,10],[13,23],[24,25]] [[1,5],[8,12],[15,24],[25,27]]Output[[1, 2], [5, 5], [8, 10], [15, 23], [24, 24], [25, 25]]

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Number of Closed Islands in C++

Arnab Chakraborty
Arnab Chakraborty
Updated on 11-Mar-2026 350 Views

Suppose we have a 2D grid consists of 0s (as land) and 1s (as water). An island is a maximal 4- directionally connected group of 0s. A closed island is an island totally surrounded by 1s. We have to find the number of closed islands. So if the grid is like1111111010000110101011101000010111111110So the output will be 2. There are two islands, that are completely surrounded by water.To solve this, we will follow these steps −Define a variable flagDefine a method called dfs, this will take the grid, i, j, n and mif i and j are not inside the range of ...

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Length of Longest Fibonacci Subsequence in C++

Arnab Chakraborty
Arnab Chakraborty
Updated on 11-Mar-2026 215 Views

Suppose we have a sequence X_1, X_2, ..., X_n is fibonacci-like if −n >= 3X_i + X_{i+1} = X_{i+2} for all i + 2 = 3 otherwise return 0.Let us see the following implementation to get better understanding −Example#include using namespace std; class Solution {    public:    int lenLongestFibSubseq(vector & A) {       int ret = 0;       unordered_map m;       int n = A.size();       vector < vector > dp(n, vector (n));       for(int i = 0; i < n; i++){         ...

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Spiral Matrix III in C++

Arnab Chakraborty
Arnab Chakraborty
Updated on 11-Mar-2026 471 Views

Suppose we have a 2 dimensional grid with R rows and C columns, we start from (r0, c0) facing east. Here, the north-west corner of the grid is at the first row and column, and the south-east corner of the grid is at the last row and column. We will walk in a clockwise spiral shape to visit every position in this grid. When we are at the outside the boundary of the grid, we continue our walk outside the grid (but may return to the grid boundary later.). We have to find a list of coordinates representing the positions ...

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Partition Array into Disjoint Intervals in C++

Arnab Chakraborty
Arnab Chakraborty
Updated on 11-Mar-2026 500 Views

Suppose we have an array A, we have to partition it into two subarrays left and right such that −Every element in left subarray is less than or equal to every element in right subarray.left and right subarrays are non-empty.left subarray has the smallest possible size.We have to find the length of left after such a partitioning. It is guaranteed that such a partitioning exists.So if the input is like [5, 0, 3, 8, 6], then the output will be 3, as left array will be [5, 0, 3] and right subarray will be [8, 6].To solve this, we will ...

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Maximum Score Words Formed by Letters in C++

Arnab Chakraborty
Arnab Chakraborty
Updated on 11-Mar-2026 310 Views

Suppose we have a list of words, a list of single letters and score for every character. We have to find the maximum score of any valid set of words formed by using the given letters.We may not use all characters in letters and each letter can only be used once. Score of letters 'a', 'b', 'c', ... ,'z' is given by score[0], score[1], ... , score[25] respectively.So, if the input is like words = ["god", "good", "toc", "cat"], letters = [a, g, o, o, d, d, d, c, t, t] and score = [5, 0, 8, 3, 0, 0, ...

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Reverse Subarray To Maximize Array Value in C++

Arnab Chakraborty
Arnab Chakraborty
Updated on 11-Mar-2026 605 Views

Suppose we have one integer array called nums. The value of this array is defined as the sum of |nums[i]-nums[i+1]| for all i in range 0 to n - 1. Where n is the size of the array. We can select any subarray of the given array and reverse it. We can perform this operation only once. Then we have to find the maximum possible value of the final array.So, if the input is like [1, 5, 4, 2, 3], then the output will be 10.To solve this, we will follow these steps −ret := 0, extra := 0n := ...

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