Interview Common Sample Codes

1. Quick Sort:

int partition(int A[], int p, int r)
{
	int x = A[r];　　// Pivot element
	int i = p - 1;　　// Index of last element that not larger than pivot element
	for(int j = p; j < r; ++j)
	{
		if(A[j] <= x)
		{
			++i;
			exchange(A[i], A[j]);
		}
	}

	exchange(A[i+1], A[r]);
	return i+1;
}

void quickSort(int A[], int p, int r)
{
	if(p >= r)	return;
	int q = partition(A, p, r);
	quickSort(A, p, q - 1);
	quickSort(A, q + 1, r);
}

2. Search in Rotated Array:

class Solution {
    int comp(int A[], int s, int e, int target){
        if(s > e) return -1;
        if(s == e) return (A[s] == target ? s : -1);

        int mid = s + (e - s) / 2;

        if(A[mid] == target)
            return mid;
        else if(A[mid] > target){
            // if first part is not rotated
            if(A[mid] >= A[s]){
                if(target >= A[s])
                    return comp(A, s, mid-1, target);
                else
                    return comp(A, mid+1, e, target);
            }else{
                return comp(A, s, mid-1, target);
            }
        }else{
            // if first part is not rotated
            if(A[mid] >= A[s]){
                return comp(A, mid+1, e, target);
            }else{
                if(target <= A[e])
                    return comp(A, mid+1, e, target);
                else
                    return comp(A, s, mid-1, target);
            }
        }
    }

public:
    int search(int A[], int n, int target) {
        return comp(A, 0, n - 1, target);
    }
};

3. Maximum Subarray:

class Solution {
public:
    int maxSubArray(int A[], int n) {
        int dp = A[0];
        int end = dp;         

        for(int i = 1; i < n; ++i){
            end = end > 0 ? end + A[i] : A[i];
            dp = dp > end ? dp : end;
        }      

        return dp;
    }
};