862. Shortest Subarray with Sum at Least K
Return the length of the shortest, non-empty, contiguous subarray of A
with sum at least K
.
If there is no non-empty subarray with sum at least K
, return -1
.
Example 1:
Input: A = [1], K = 1
Output: 1
Example 2:
Input: A = [1,2], K = 4
Output: -1
Example 3:
Input: A = [2,-1,2], K = 3
Output: 3
Note:
1 <= A.length <= 50000
-10 ^ 5 <= A[i] <= 10 ^ 5
1 <= K <= 10 ^ 9
Approach #1: prefix sum. [Time Limit Exceeded]
class Solution {
public:
int shortestSubarray(vector<int>& A, int K) {
int len = A.size();
if (len == 1 && A[0] >= K) return 1;
int step = INT_MAX;
vector<int> prefixSum(len, 0);
prefixSum[0] = A[0];
for (int i = 1; i < len; ++i)
prefixSum[i] = prefixSum[i-1] + A[i];
for (int i = 0; i < len; ++i) {
if (prefixSum[i] >= K)
step = min(step, i+1);
for (int j = i+1; j < len; ++j) {
if (prefixSum[j]-prefixSum[i] >= K) {
step = min(step, j-i);
}
}
}
if (step == INT_MAX) return -1;
else return step;
}
};
Approach #2: deque.
class Solution {
public:
int shortestSubarray(vector<int>& A, int K) {
int len = A.size();
int res = len + 1;
vector<int> sum(len+1, 0);
for (int i = 0; i < len; ++i)
sum[i+1] = sum[i] + A[i];
deque<int> d;
for (int i = 0; i < len+1; ++i) {
while (!d.empty() && sum[i]-sum[d.front()] >= K)
res = min(res, i-d.front()), d.pop_front();
while (!d.empty() && sum[i] <= sum[d.back()])
d.pop_back();
d.push_back(i);
}
return res <= len ? res : -1;
}
};
Runtime: 144 ms, faster than 33.12% of C++ online submissions for Shortest Subarray with Sum at Least K.
Analysis:
deque Member functions
- (constructor)
- Construct deque container (public member function )
- (destructor)
- Deque destructor (public member function )
- operator=
- Assign content (public member function )
Iterators:
- begin
- Return iterator to beginning (public member function )
- end
- Return iterator to end (public member function )
- rbegin
- Return reverse iterator to reverse beginning (public member function )
- rend
- Return reverse iterator to reverse end (public member function )
- cbegin
- Return const_iterator to beginning (public member function )
- cend
- Return const_iterator to end (public member function )
- crbegin
- Return const_reverse_iterator to reverse beginning (public member function )
- crend
- Return const_reverse_iterator to reverse end (public member function )
Capacity:
- size
- Return size (public member function )
- max_size
- Return maximum size (public member function )
- resize
- Change size (public member function )
- empty
- Test whether container is empty (public member function )
- shrink_to_fit
- Shrink to fit (public member function )
Element access:
- operator[]
- Access element (public member function )
- at
- Access element (public member function )
- front
- Access first element (public member function )
- back
- Access last element (public member function )
Modifiers:
- assign
- Assign container content (public member function )
- push_back
- Add element at the end (public member function )
- push_front
- Insert element at beginning (public member function )
- pop_back
- Delete last element (public member function )
- pop_front
- Delete first element (public member function )
- insert
- Insert elements (public member function )
- erase
- Erase elements (public member function )
- swap
- Swap content (public member function )
- clear
- Clear content (public member function )
- emplace
- Construct and insert element (public member function )
- emplace_front
- Construct and insert element at beginning (public member function )
- emplace_back
- Construct and insert element at the end (public member function )
Allocator:
- get_allocator
- Get allocator (public member function )
Non-member functions overloads
- relational operators
- Relational operators for deque (function )
- swap
- Exchanges the contents of two deque containers (function template )
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