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698.cpp
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class Solution {
// Runtime: 16 ms, faster than 44.02% of C++ online submissions for Partition
// to K Equal Sum Subsets. Memory Usage: 8.3 MB, less than 61.79% of C++
// online submissions for Partition to K Equal Sum Subsets.
public:
bool canPartitionKSubsets(vector<int> &nums, int k) {
int sum = accumulate(begin(nums), end(nums), 0);
if (k <= 0 or sum % k != 0)
return false;
vector<int> visited(nums.size(), 0);
int target = sum / k;
function<bool(int, int, int)> canPartition = [&](int start_index, int k,
int cur_sum) {
if (k == 1)
return true;
if (cur_sum == target)
return canPartition(0, k - 1, 0);
for (int i = start_index; i < nums.size(); i++)
if (!visited[i]) {
visited[i] = 1;
if (canPartition(i + 1, k, cur_sum + nums[i]))
return true;
visited[i] = 0;
}
return false;
};
return canPartition(0, k, 0);
}
};
class Solution2 {
// Runtime: 0 ms
// Memory Usage: 8.2 MB
public:
bool canPartitionKSubsets(vector<int> &nums, int k) {
int sum = accumulate(begin(nums), end(nums), 0);
sort(nums.begin(), nums.end(), greater<int>());
if (sum % k != 0)
return false;
int target = sum / k;
vector<int> buckets(k, 0);
function<bool(int)> dfs = [&](int idx) {
if (idx == nums.size()) {
for (auto num : buckets)
if (num != target)
return false;
return true;
}
for (auto &val : buckets) {
int curr = nums[idx];
if (curr + val > target)
continue;
val += curr;
if (dfs(idx + 1))
return true;
val -= curr;
if (val == 0)
break;
}
return false;
};
return dfs(0);
}
};