Add solutions of mine

unk2001/unk2001_Counting_Bits.cpp

@@ -0,0 +1,42 @@
+// Word Combinations
+// cses.fi/1146
+#include <bits/stdc++.h>
+
+using namespace std;
+typedef long long ll;
+
+ll n;
+
+ll get(int sz) {
+    return 1ll*sz*(1ll << (sz-1));
+}
+int main() {
+    ios_base::sync_with_stdio(0); cin.tie(0); 
+    cin >> n;
+
+    vector<int> binary;
+    while (n) {
+        binary.push_back(n % 2);
+        n /= 2;
+    }
+    reverse(binary.begin(), binary.end());
+    ll res = 0;
+    int len = binary.size();
+    for (int i = 1; i <= binary.size(); i++) {
+        int x = binary[i-1];
+        if (x == 0) continue;
+        res += get(len - i);
+    }
+
+    ll order = 0;
+    for (int i = binary.size(); i >= 1; i--) {
+        int x = binary[i-1];
+        if (x == 0) continue;
+        res += order;
+        order += (1ll << (len-i));
+    }
+    for (auto x : binary) res += x;
+    cout <<res;
+}
+// author: unk2001
+// profile: https://cses.fi/user/13599

unk2001/unk2001_Shortest_Subsequence.cpp

@@ -0,0 +1,49 @@
+// Word Combinations
+// cses.fi/1087
+#include <bits/stdc++.h>
+#define FOR(i, u, v) for (int i = u; i <= v; i++)
+#define FORD(i, v, u) for (int i = v; i >= u; i--)
+#define pii pair<int, int>
+#define mp make_pair
+#define F first
+#define S second
+#define PB push_back
+#define N 1000005
+
+using namespace std;
+
+string s;
+int n, nxt[N][4];
+
+string DNA = "ACGT";
+
+int main() {
+    ios_base::sync_with_stdio(0); cin.tie(0); 
+
+    cin >> s;
+    n = s.size();
+    s = " " + s;
+    FOR(i, 0, 3) nxt[n+1][i] = n+1;
+    FORD(i, n, 1) {
+        FOR(j, 0, 3) nxt[i][j] = nxt[i+1][j];
+        int x = DNA.find(s[i]);
+        nxt[i][x] = i;
+    }
+
+    string ans = "";
+    int curPos = 1;
+    while (curPos <= n+1) {
+        int best = 0;
+        FOR(j, 1, 3) {
+            if (nxt[curPos][j] > nxt[curPos][best]) {
+                best = j;
+            }
+        }
+        curPos = nxt[curPos][best];
+        ans.push_back(DNA[best]);
+        curPos++;
+    }
+    cout <<ans;
+}
+// author: unk2001
+// profile: https://cses.fi/user/13599

unk2001/unk2001_Tree_Diameter.cpp

@@ -0,0 +1,46 @@
+// Word Combinations
+// cses.fi/1131
+#include <bits/stdc++.h>
+
+using namespace std;
+const int N = 200006;
+
+int n;
+vector<int> g[N];
+
+pair<int, int>  BFS(int pivot) {
+    queue<int> q;
+    vector<int> d(n+1, -1);
+    d[pivot] = 0; q.push(pivot);
+
+    while (!q.empty()) {
+        int u = q.front();
+        q.pop();
+        for (auto v : g[u]) {
+            if (d[v] == -1) {
+                d[v] = d[u] + 1;
+                q.push(v);
+            }
+        }
+    }
+    for (int i = 1; i <= n; i++) {
+        if (d[pivot] < d[i]) {
+            pivot = i;
+        }
+    }
+    return make_pair(pivot, d[pivot]);
+}
+int main() {
+    ios_base::sync_with_stdio(0); cin.tie(0);
+    cin >> n;
+    for (int i = 1; i < n; i++) {
+        int u, v; cin >> u >> v;
+        g[u].push_back(v);
+        g[v].push_back(u);
+    }
+    auto z1 = BFS(1);
+    auto z2 = BFS(z1.first);
+    cout <<z2.second;
+}
+// author: unk2001
+// profile: https://cses.fi/user/13599

unk2001/unk2001_Word_Combinations.cpp

@@ -0,0 +1,85 @@
+// Word Combinations
+// cses.fi/1731
+#include <bits/stdc++.h>
+
+using namespace std;
+
+const int N = 5005;
+
+struct Node {
+    Node *child[26];
+    bool isWord;
+    Node() {
+        for (int i = 0; i < 26; i++) {
+            child[i] = NULL;
+        }
+        isWord = false;
+    }
+};
+
+struct Trie {
+    Node *root;
+
+    Trie() {
+        root = new Node();
+    }
+
+    Node* getRoot() {
+        return root;
+    }
+    Node* getNext(Node *p, char c) {
+        if (p->child[c-'a'] == NULL) {
+            return NULL;
+        } else {
+            return p->child[c-'a'];
+        }
+    }
+
+    void addWord(string s) {
+        Node *p = root;
+        for (auto c : s) {
+            if (p->child[c-'a'] == NULL) {
+                p->child[c-'a'] = new Node();
+            }
+            p = p->child[c-'a'];
+        }
+        p->isWord = true;
+    }
+}trie;
+
+int n, m, dp[N];
+string s;
+
+const int mod = 1000000007;
+void inline add(int &A, int B) {
+    A += B;
+    if (A >= mod) A -= mod;
+}
+int main() {
+    ios_base::sync_with_stdio(0); cin.tie(0); 
+    cin >> s;
+    n = s.size(); s = " " + s;
+    cin >> m;
+    for (int i = 1; i <= m; i++) {
+        string t; cin >> t;
+        reverse(t.begin(), t.end());
+        trie.addWord(t);
+    }
+
+    dp[0] = 1;
+    for (int i = 1; i <= n; i++) {
+        Node *p = trie.getRoot();
+        for (int j = i; j >= 1; j--) {
+            p = trie.getNext(p, s[j]);
+            if (p == NULL) {
+                break;
+            } else if (p->isWord == true) {
+                add(dp[i], dp[j-1]);
+            }
+        }
+    }
+    cout <<dp[n];
+}
+
+// author: unk2001
+// profile: https://cses.fi/user/13599