494. Target Sum
Đề Bài
You are given an integer array nums and an integer target.
You want to build an expression out of nums by adding one of the symbols '+' and '-' before each integer in nums and then concatenate all the integers.
- For example, if
nums = [2, 1], you can add a'+'before2and a'-'before1and concatenate them to build the expression"+2-1".
Return the number of different expressions that you can build, which evaluates to target.
Example 1:
Input: nums = [1,1,1,1,1], target = 3 Output: 5 Explanation: There are 5 ways to assign symbols to make the sum of nums be target 3. -1 + 1 + 1 + 1 + 1 = 3 +1 - 1 + 1 + 1 + 1 = 3 +1 + 1 - 1 + 1 + 1 = 3 +1 + 1 + 1 - 1 + 1 = 3 +1 + 1 + 1 + 1 - 1 = 3
Example 2:
Input: nums = [1], target = 1 Output: 1
Constraints:
1 <= nums.length <= 200 <= nums[i] <= 10000 <= sum(nums[i]) <= 1000-1000 <= target <= 1000
Thuật Toán & Kỹ Thuật
⏱️ Thời gian
O(V+E)
💾 Không gian
O(V)
Lời Giải
C++
0494-target-sum.cpp
class Solution {
private:
int n;
public:
int dfs(vector<int>& nums, int target, int i) {
if (i == n) {
return target == 0;
}
int cnt = 0;
cnt += dfs(nums, target - nums[i], i + 1);
cnt += dfs(nums, target + nums[i], i + 1);
return cnt;
}
int findTargetSumWays(vector<int>& nums, int target) {
n = nums.size();
return dfs(nums, target, 0);
}
};