leetcode

Some graph problems - Union_Find.cpp * Union by size instead of rank, useful for some problems

6 files changed, 202 insertions(+), 7 deletions(-)

diff --git a/ Problems/0851.cpp b/ Problems/0851.cpp

@@ -0,0 +1,29 @@

class Solution {

public:

vector<int> loudAndRich(vector<vector<int>> &richer, vector<int> &quiet) {

const int n = quiet.size();

vector<vector<int>> adj(n);

vector<int> count(n);

vector<int> res(n);

iota(res.begin(), res.end(), 0);

for (auto &p : richer) {

adj[p[0]].push_back(p[1]);

count[p[1]]++;

}

queue<int> q;

for (int i = 0; i < n; i++)

if (!count[i]) q.push(i);

while (!q.empty()) {

int crnt = q.front();

q.pop();

for (int &c : adj[crnt]) {

if (quiet[res[c]] > quiet[res[crnt]]) res[c] = res[crnt];

if (!--count[c]) q.push(c);

}

}

return res;

}

};

diff --git a/ Problems/1462.cpp b/ Problems/1462.cpp

@@ -0,0 +1,103 @@

// DFS

class Solution {

public:

vector<bool> checkIfPrerequisite(int numCourses,

vector<vector<int>> &prerequisites,

vector<vector<int>> &queries) {

vector<vector<int>> adj(numCourses);

vector<unordered_set<int>> pre(numCourses);

for (auto &p : prerequisites) adj[p[0]].push_back(p[1]);

for (int i = 0; i < numCourses; i++) {

unordered_set<int> visited;

stack<int> st;

st.push(i);

visited.insert(i);

while (!st.empty()) {

int crnt = st.top();

st.pop();

for (int &c : adj[crnt]) {

if (visited.count(c)) continue;

visited.insert(c);

pre[c].insert(i);

st.push(c);

}

}

}

vector<bool> res;

for (auto &p : queries) res.push_back(pre[p[1]].count(p[0]));

return res;

}

};

// Topological sort with dependency propagation

class Solution {

public:

vector<bool> checkIfPrerequisite(int numCourses,

vector<vector<int>> &prerequisites,

vector<vector<int>> &queries) {

vector<unordered_set<int>> pre(numCourses);

vector<vector<int>> adj(numCourses);

vector<int> count(numCourses);

for (auto &p : prerequisites) {

adj[p[0]].push_back(p[1]);

count[p[1]]++;

}

queue<int> q;

for (int i = 0; i < numCourses; i++)

if (!count[i]) q.push(i);

while (!q.empty()) {

int crnt = q.front();

q.pop();

for (int &c : adj[crnt]) {

pre[c].insert(crnt);

pre[c].insert(pre[crnt].begin(), pre[crnt].end());

if (!--count[c]) q.push(c);

}

}

vector<bool> res;

for (auto &p : queries) res.push_back(pre[p[1]].count(p[0]));

return res;

}

};

// Topological sort using bitseclass Solution {

public:

vector<bool> checkIfPrerequisite(int numCourses,

vector<vector<int>> &prerequisites,

vector<vector<int>> &queries) {

vector<bitset<100>> pre(numCourses);

vector<vector<int>> adj(numCourses);

vector<int> count(numCourses);

for (auto &p : prerequisites) {

adj[p[0]].push_back(p[1]);

count[p[1]]++;

}

queue<int> q;

for (int i = 0; i < numCourses; i++)

if (!count[i]) q.push(i);

while (!q.empty()) {

int crnt = q.front();

q.pop();

for (int &c : adj[crnt]) {

pre[c].set(crnt);

pre[c] |= pre[crnt];

if (!--count[c]) q.push(c);

}

}

vector<bool> res;

for (auto &p : queries) res.push_back(pre[p[1]][p[0]]);

return res;

}

}

;

diff --git a/ Problems/2244.cpp b/ Problems/2244.cpp

@@ -0,0 +1,14 @@

class Solution {

public:

int minimumRounds(vector<int> &tasks) {

unordered_map<int, int> um;

for (int t : tasks) um[t]++;

int round = 0;

for (auto [_, c] : um) {

if (c == 1) return -1;

round += (c - 1) / 3 + 1;

}

return round;

}

};

diff --git a/ Problems/2316.cpp b/ Problems/2316.cpp

@@ -0,0 +1,45 @@

class UnionFind {

int n, cnt = n;

vector<int> root, size;

public:

UnionFind(int n) : n(n), root(n), size(n, 1) {

iota(root.begin(), root.end(), 0);

}

int find(int x) {

while (x != root[x]) x = root[x] = root[root[x]];

return x;

}

void join(int x, int y) {

x = find(x), y = find(y);

if (x != y) {

if (size[x] > size[y]) swap(x, y);

root[x] = y;

size[y] += size[x];

cnt--;

}

}

int count() { return cnt; }

bool connected(int x, int y) { return find(x) == find(y); }

long long count_unreachable() {

long long res = 0;

for (int i = 0; i < n; i++)

if (root[i] == i) res += (long long)size[i] * (n - size[i]);

return res / 2;

}

};

class Solution {

public:

long long countPairs(int n, vector<vector<int>> &edges) {

UnionFind uf(n);

for (auto &e : edges) uf.join(e[0], e[1]);

return uf.count_unreachable();

}

};

diff --git a/ README.md b/ README.md

@@ -182,6 +182,7 @@ for solving problems. | 0830 | Medium | [Kth Smallest Element in a BST](Problems/0230.cpp) | | 0841 | Medium | [Keys and Rooms](Problems/0841.cpp) | | 0844 | Easy | [Backspace String Compare](Problems/0844.cpp) |

| 0851 | Medium | [Loud and Rich](Problems/0851.cpp) |

| 0872 | Easy | [Leaf-Similar Trees](Problems/0872.cpp) | | 0876 | Easy | [Middle of the Linked List](Problems/0876.cpp) | | 0886 | Medium | [Possible Bipartition](Problems/0886.cpp) |

@@ -235,6 +236,7 @@ for solving problems. | 1382 | Medium | [Balance a Binary Search Tree](Problems/1382.cpp) | | 1425 | Hard | [Constrained Subsequence Sum](Problems/1425.cpp) | | 1438 | Medium | [Longest Continuous Subarray With Absolute Diff Less Than or Equal to Limit](Problems/0143.cpp) |

| 1462 | Medium | [Course Schedule IV](Problems/1462.cpp) |

| 1466 | Medium | [Reorder Routes to Make All Paths Lead to the City Zero](Problems/1466.cpp) | | 1472 | Medium | [Design Browser History ](Problems/1472.cpp) | | 1480 | Easy | [Running Sum of 1d Array](Problems/1480.cpp) |

@@ -270,9 +272,11 @@ for solving problems. | 2192 | Medium | [All Ancestors of a Node in a Directed Acyclic Graph](Problems/2192.cpp) | | 2235 | Easy | [Add Two Integers](Problems/2235.cpp) | | 2236 | Easy | [Root Equals Sum of Children](Problems/2236.cpp) |

| 2244 | Medium | [Minimum Rounds to Complete All Tasks](Problems/2244.cpp) |

| 2265 | Medium | [Count Nodes Equal to Average of Subtree](Problems/2265.cpp) | | 2279 | Medium | [Maximum Bags With Full Capacity of Rocks](Problems/2279.cpp) | | 2285 | Medium | [Maximum Total Importance of Roads](Problems/2285.cpp) |

| 2316 | Medium | [Count Unreachable Pairs of Nodes in an Undirected Graph](Problems/2316.cpp) |

| 2326 | Medium | [Spiral Matrix IV](Problems/2326.cpp) | | 2331 | Easy | [Evaluate Boolean Binary Tree](Problems/2331.cpp) | | 2368 | Medium | [Reachable Nodes With Restrictions](Problems/2368.cpp) |

diff --git a/ Templates/Union_Find.cpp b/ Templates/Union_Find.cpp

@@ -1,9 +1,9 @@ class UnionFind {

int n;

vector<int> root, rank;

int n, cnt = n;

vector<int> root, size;

public:

UnionFind(int n) : n(n), root(n), rank(n, 1) {

UnionFind(int n) : n(n), root(n), size(n, 1) {

iota(root.begin(), root.end(), 0); }

@@ -15,13 +15,13 @@ public: void join(int x, int y) { x = find(x), y = find(y); if (x != y) {

if (rank[x] > rank[y]) swap(x, y);

if (size[x] > size[y]) swap(x, y);

root[x] = y;

rank[y] += 1;

n--;

size[y] += size[x];

cnt--;

} }

int count() { return n; }

int count() { return cnt; }

bool connected(int x, int y) { return find(x) == find(y); } };