Hi I am trying to practice c and came across a error while solving a problem, I am using vectors in my code and getting error where I added two elements in vector through reference operator'[]'

C

class Solution {
public:
    vector<int> twoSum(vector<int>& nums, int target) {
        vector<int> temp;
        int p = 0;
        for (auto i = nums.begin(); i != (nums.end() - 1);   i) {
            cout<<*i;
            p = nums[i] nums[i 1];                 //Error is in this line
            if ((p) == target) {
                temp.push_back(i);
                temp.push_back(i   1);
                return temp;
            }
        }
    }
};

Error: No viable overloaded operator[] for type vector

CodePudding user response：

i is an iterator, not an index, so you don't need [] at all.

class Solution {
public:
    std::vector<int> twoSum(std::vector<int>& nums, int target) {
        for (auto i = nums.begin(); i != (nums.end() - 1);   i) {
            std::cout<<*i;
            if ((*i   *(i   1)) == target) {
                return { *i, *(i   1) };
            }
        }
        throw std::runtime_error("no solution found");
    }
};

However rather than writing the loop yourself, you could use the existing std::adjacent_find

class Solution {
public:
    std::vector<int> twoSum(std::vector<int>& nums, int target) {
        auto i = std::adjacent_find(nums.begin(), nums.end(), [target](int a, int b) { 
            std::cout << a;
            return (a   b) == target; 
        });
        if (i != nums.end()) {
            return { *i, *(i   1) };
        }
        throw std::runtime_error("no solution found");
    }
};

CodePudding user response：

I fixed your code, you cannot mix iterators with numeric values.

class Solution {
public:
    vector<int> twoSum(vector<int>& nums, int target) {
        vector<int> temp;
        int p = 0;
        for (auto i = nums.begin(); i != (nums.end() - 1);   i) {
            cout << *i;
            p = *i   *(i   1);                 //now code works fine 
            if ((p) == target) {
                temp.push_back(*i);
                temp.push_back(*(i   1));
                return temp;

            }
        }


    }
};

when you use loop using iterators you shouldn't access into a vector via [] operator, because iterators are pointers to elements of the vector. simply use *i to access value iterator points to.