Question

How to increment an integer represented as an integer vector of digits by one in C++

Answer 1

#include <iostream>
#include <vector>

std::vector<int> incrementByOne(std::vector<int>& digits) {
    int size = digits.size();
    int carry = 1; // Start with the increment of 1

    for (int i = size - 1; i >= 0; i--) {
        digits[i] += carry;
        if (digits[i] == 10) {
            digits[i] = 0; // Reset to 0 if there's a carry
            carry = 1;     // Carry over to the next digit
        } else {
            carry = 0;     // No carry, break early
            break;
        }
    }

    if (carry == 1) {
        digits.insert(digits.begin(), 1); // Add a new digit at the front
    }

    return digits;
}

int main() {
    std::vector<int> digits = {9, 9, 9}; 
    
    incrementByOne(digits);

    std::cout << "Result: ";
    for (int digit : digits) {
        std::cout << digit << " ";
    }
    std::cout << std::endl;
}


/*
run:

Result: 1 0 0 0 

*/

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