Solve problems 981[A, B, C] from codeforces

Author: AliOsm

CodeForces/981A. Antipalindrome.cpp

@@ -0,0 +1,27 @@
+/*
+	Idea:
+		- Brute force, try every possible substring.
+*/
+
+#include <bits/stdc++.h>
+
+using namespace std;
+
+int main() {
+  string s;
+  cin >> s;
+
+  int mx = 0;
+  for(int i = 0; i < s.length(); ++i) {
+  	for(int j = 1; j <= s.length(); ++j) {
+  		string tmp = s.substr(i, j), rev = tmp;
+  		reverse(rev.begin(), rev.end());
+  		if(tmp != rev)
+  			mx = max(mx, int(tmp.length()));
+  	}
+  }
+
+  cout << mx << endl;
+
+  return 0;
+}

CodeForces/981B. Businessmen Problems.cpp

@@ -0,0 +1,46 @@
+/*
+  Idea:
+    - Greedy, for each value in each company choose the largest one.
+*/
+
+#include <bits/stdc++.h>
+
+using namespace std;
+
+int const N = 1e5 + 1;
+int n, m;
+map<int, int> a, b;
+vector<int> all;
+
+int main() {
+  scanf("%d", &n);
+  for(int i = 0, x, y; i < n; ++i) {
+  	scanf("%d %d", &x, &y);
+  	a[x] = y;
+  	all.push_back(x);
+  }
+
+	scanf("%d", &m);
+  for(int i = 0, x, y; i < m; ++i) {
+  	scanf("%d %d", &x, &y);
+  	b[x] = y;
+  	all.push_back(x);
+  }
+
+  sort(all.begin(), all.end());
+  all.resize(unique(all.begin(), all.end()) - all.begin());
+
+  long long res = 0;
+  for(int i = 0, mx; i < all.size(); ++i) {
+  	mx = 0;
+  	if(a.count(all[i]))
+  		mx = max(mx, a[all[i]]);
+  	if(b.count(all[i]))
+  		mx = max(mx, b[all[i]]);
+  	res += mx;
+  }
+
+  printf("%lld\n", res);
+
+  return 0;
+}

CodeForces/981C. Useful Decomposition.cpp

@@ -0,0 +1,82 @@
+/*
+  Idea:
+    - Greedy, there is a solution if and only if the tree is a single path
+      or there is one node has more than two edges go from it to another nodes.
+*/
+
+#include <bits/stdc++.h>
+
+using namespace std;
+
+int const N = 1e5 + 1;
+int n;
+bool vis[N];
+vector<vector<int> > g;
+vector<int> sol;
+
+void DFS(int u) {
+  vis[u] = true;
+
+  bool ok = false;
+  for(int i = 0, v; i < g[u].size(); ++i) {
+    v = g[u][i];
+    if(!vis[v]) {
+      ok = true;
+      DFS(v);
+    }
+  }
+
+  if(!ok)
+    sol.push_back(u + 1);
+}
+
+int main() {
+  scanf("%d", &n);
+  g.resize(n);
+  for(int i = 0, a, b; i < n - 1; ++i) {
+    scanf("%d %d", &a, &b);
+    --a, --b;
+    g[a].push_back(b);
+    swap(a, b);
+    g[a].push_back(b);
+  }
+
+  int gt2 = 0;
+  for(int i = 0; i < n; ++i)
+    if(g[i].size() > 2)
+      ++gt2;
+
+  if(gt2 > 1) {
+    puts("No");
+    return 0;
+  }
+
+  puts("Yes");
+
+  if(gt2 == 0) {
+    puts("1");
+    for(int i = 0; i < g.size(); ++i)
+      if(g[i].size() == 1)
+        printf("%d ", i + 1);
+    puts("");
+    return 0;
+  }
+
+  int mx = 0, idx;
+  for(int i = 0; i < n; ++i) {
+    if(g[i].size() > mx) {
+      mx = g[i].size();
+      idx = i;
+    }
+  }
+
+  printf("%d\n", mx);
+
+  DFS(idx);
+  ++idx;
+
+  for(int i = 0; i < sol.size(); ++i)
+    printf("%d %d\n", idx, sol[i]);
+
+  return 0;
+}

CodeForces/README.md

@@ -430,6 +430,9 @@
 - [979A. Pizza, Pizza, Pizza!!!](http://codeforces.com/contest/979/problem/A)
 - [979B. Treasure Hunt](http://codeforces.com/contest/979/problem/B)
 - [979C. Kuro and Walking Route](http://codeforces.com/contest/979/problem/C)
+- [981A. Antipalindrome](http://codeforces.com/contest/981/problem/A)
+- [981B. Businessmen Problems](http://codeforces.com/contest/981/problem/B)
+- [981C. Useful Decomposition](http://codeforces.com/contest/981/problem/C)
 - [982A. Row](http://codeforces.com/contest/982/problem/A)
 - [982B. Bus of Characters](http://codeforces.com/contest/982/problem/B)
 - [982C. Cut 'em all!](http://codeforces.com/contest/982/problem/C)