377. Combination Sum IV
Đề Bài
Given an array of distinct integers nums and a target integer target, return the number of possible combinations that add up to target.
The test cases are generated so that the answer can fit in a 32-bit integer.
Example 1:
Input: nums = [1,2,3], target = 4 Output: 7 Explanation: The possible combination ways are: (1, 1, 1, 1) (1, 1, 2) (1, 2, 1) (1, 3) (2, 1, 1) (2, 2) (3, 1) Note that different sequences are counted as different combinations.
Example 2:
Input: nums = [9], target = 3 Output: 0
Constraints:
1 <= nums.length <= 2001 <= nums[i] <= 1000- All the elements of
numsare unique. 1 <= target <= 1000
Follow up: What if negative numbers are allowed in the given array? How does it change the problem? What limitation we need to add to the question to allow negative numbers?
Thuật Toán & Kỹ Thuật
⏱️ Thời gian
O(n²)
💾 Không gian
O(n)
Lời Giải
C++
0377-combination-sum-iv.cpp
class Solution {
public:
int combinationSum4(vector<int>& nums, int target) {
vector<uint> dp(target + 1);
dp[0] = 1;
for (int i = 1; i <= target; ++i) {
for (int num : nums) {
if (i - num >= 0) {
dp[i] += dp[i - num];
}
}
}
return dp[target];
}
};