leetcode

Improved Daily Problem

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;

}

};