leetcode

Solution to some Leetcode problems written in C++
git clone git://git.dimitrijedobrota.com/leetcode.git
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commitdd63796ba7593aa00c2713806779db89a2da630b
parented4d5136e5d7161ea0da3b487d41bf822855c3a4
authorDimitrije Dobrota <mail@dimitrijedobrota.com>
dateTue, 1 Aug 2023 18:50:46 +0200

Improved Daily Problem

Diffstat:
MProblems/0077.cpp|+++++++++++++++++++++++++++++++++++++++++++++++++++++-----

1 files changed, 53 insertions(+), 5 deletions(-)

diff --git a/Problems/0077.cpp b/Problems/0077.cpp

@@ -1,16 +1,18 @@

// Recursive solution
class Solution {
vector<int> crnt;
vector<vector<int>> res;
void rec(int s, int n, int k) {
if (s > n + 1) return;
if (!k) {
res.push_back(crnt);
return;
}
for (int i = s; i <= n; i++) {
crnt.push_back(i);
rec(i + 1, n, k - 1);
crnt.pop_back();
}
crnt.push_back(s);
rec(s + 1, n, k - 1);
crnt.pop_back();
rec(s + 1, n, k);
}
public:

@@ -19,3 +21,49 @@ public:

return res;
}
};
// Iterative solution
class Solution {
public:
vector<vector<int>> combine(int n, int k) {
vector<vector<int>> res;
vector<int> iter;
iter.reserve(k);
for (int mask = (1 << k) - 1; mask < 1 << n; mask++) {
if (__builtin_popcount(mask) != k) continue;
for (int crnt = mask, idx; crnt; crnt ^= 1 << (idx - 1)) {
idx = __builtin_ffs(crnt);
iter.push_back(idx);
}
res.push_back(iter);
iter.clear();
}
return res;
}
};
// Improved iterative solution with bit twiddling
class Solution {
int twiddle(int v) {
int t = v | (v - 1);
int w = (t + 1) | (((~t & -~t) - 1) >> (__builtin_ctz(v) + 1));
return w;
}
public:
vector<vector<int>> combine(int n, int k) {
vector<vector<int>> res;
vector<int> iter;
iter.reserve(k);
for (int mask = (1 << k) - 1; mask < 1 << n; mask = twiddle(mask)) {
for (int crnt = mask, idx; crnt; crnt ^= 1 << (idx - 1)) {
idx = __builtin_ffs(crnt);
iter.push_back(idx);
}
res.push_back(iter);
iter.clear();
}
return res;
}
};