Examples to Understand Time Complexity.

TimeComplexityExample2.cpp

int sum(vector<int> nums) {
    int ans = 0;                          // 1
    for (int i=0; i<nums.size(); i++) {   // n times
        ans += nums[i];                   // 1
    }
    return ans;                           // 1
}

void efficient(vector<int> nums) {
    int addition = sum(nums);             // O(n). Note: Single line does not 
                                          // mean constant time.
    for (int i=0; i<n; i++) {             // n times
        nums[i] = nums[i] + addition;     // 1
     }
}

void inefficient(vector<int> nums) { 
    for (int i=0; i<n; i++) {             // n times
        nums[i] = nums[i] +  sum(nums);   // O(n)
     }
}