leetcode

Algorithm II: Day 8

4 files changed, 123 insertions(+), 2 deletions(-)

diff --git a/ Problems/0130.cpp b/ Problems/0130.cpp

@@ -0,0 +1,53 @@

class Solution {

typedef vector<vector<char>> Matrix;

typedef queue<pair<int, int>> Queue;

const vector<pair<int, int>> offsets = {

{ 0, 1},

{ 0, -1},

{ 1, 0},

{-1, 0}

};

int n, m;

int valid(int x, int y) { return x >= 0 && x < n && y >= 0 && y < m; }

void dfs(Matrix &board, int x, int y) {

Queue q;

q.push({x, y}), board[x][y] = '#';

while (!q.empty()) {

auto [a, b] = q.front();

q.pop();

for (auto [oa, ob] : offsets) {

int x = a + oa, y = b + ob;

if (!valid(x, y) || board[x][y] == 'X' || board[x][y] != 'O') continue;

board[x][y] = '#';

q.push({x, y});

}

}

}

public:

void solve(Matrix &board) {

n = board.size(), m = board[0].size();

unordered_set<int> convert;

Queue q;

int group = 0;

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

if (board[i][0] == 'O') dfs(board, i, 0);

if (board[i][m - 1] == 'O') dfs(board, i, m - 1);

}

for (int j = 0; j < m; j++) {

if (board[0][j] == 'O') dfs(board, 0, j);

if (board[n - 1][j] == 'O') dfs(board, n - 1, j);

}

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

for (int j = 0; j < m; j++)

if (board[i][j] != 'X') board[i][j] = board[i][j] == 'O' ? 'X' : 'O';

}

};

diff --git a/ Problems/1091.cpp b/ Problems/1091.cpp

@@ -0,0 +1,36 @@

class Solution {

int n;

bool valid(int x, int y) { return x >= 0 && x < n && y >= 0 && y < n; }

public:

int shortestPathBinaryMatrix(vector<vector<int>> &grid) {

if (grid[0][0] == 1 || grid.back().back() == 1) return -1;

n = grid.size();

queue<pair<int, int>> q;

q.push({0, 0});

vector<pair<int, int>> offsets = {

{-1, 0},

{-1, 1},

{ 0, 1},

{ 1, 1},

{ 1, 0},

{ 1, -1},

{ 0, -1},

{-1, -1}

};

while (!q.empty()) {

auto [a, b] = q.front();

q.pop();

if (a == n - 1 && b == n - 1) return grid[a][b] + 1;

for (auto [ox, oy] : offsets) {

int x = a + ox, y = b + oy;

if (!valid(x, y) || grid[x][y] > 0) continue;

grid[x][y] = grid[a][b] + 1;

q.push({x, y});

}

}

return -1;

}

};

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

@@ -15,9 +15,10 @@ if you have any questions. I have accumulated a list of most commonly used algorithms to serve as a base for solving problems.

* [Union Find](Templates/Union_Find.cpp)

* [MST from edge vector](Templates/MST_vector.cpp)

* [MST from edge priority queue](Templates/MST_pq.cpp)

* [MST from edge vector](Templates/MST_vector.cpp)

* [Matrix BFS/Flood fill](Templates/bfs_floodfill.cpp)

* [Union Find](Templates/Union_Find.cpp)

## Problems

@@ -103,6 +104,7 @@ for solving problems. | 0125 | Easy | [Valid Palindrome](Problems/0125.cpp) | | 0128 | Medium | [Longest Consecutive Sequence](Problems/0128.cpp) | | 0129 | Medium | [Sum Root to Leaf Numbers](Problems/0129.cpp) |

| 0130 | Medium | [Surrounded Regions](Problems/0130.cpp) |

| 0131 | Medium | [Palindrome Partitioning](Problems/0131.cpp) | | 0133 | Medium | [Clone Graph](Problems/0133.cpp) | | 0134 | Medium | [Gas Station](Problems/0134.cpp) |

@@ -323,6 +325,7 @@ for solving problems. | 1061 | Medium | [Lexicographically Smallest Equivalent String](Problems/1061.cpp) | | 1071 | Easy | [Greatest Common Divisor of Strings](Problems/1071.cpp) | | 1089 | Easy | [Duplicate Zeros](Problems/1089.cpp) |

| 1091 | Medium | [Shortest Path in Binary Matrix](Problems/1091.cpp) |

| 1095 | Easy | [Find Numbers with Even Number of Digits](Problems/1095.cpp) | | 1099 | Easy | [Replace Elements with Greatest Element on Right Side](Problems/1099.cpp) | | 1129 | Medium | [Shortest Path with Alternating Colors](Problems/1129.cpp) |

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

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

// Matrix BFS/Flood fill

typedef vector<vector<int>> Matrix;

typedef queue<pair<int, int>> Queue;

const vector<pair<int, int>> offsets = {

{ 0, 1},

{ 0, -1},

{ 1, 0},

{-1, 0}

};

int n, m;

int valid(int x, int y) { return x >= 0 && x < n && y >= 0 && y < m; }

void dfs(Matrix &mat, int x, int y) {

Queue q;

q.push({x, y}), mat[x][y] = 2;

while (!q.empty()) {

auto [a, b] = q.front();

q.pop();

for (auto [oa, ob] : offsets) {

int x = a + oa, y = b + ob;

if (!valid(x, y) || mat[x][y] == 0 || mat[x][y] != 1) continue;

mat[x][y] = 2;

q.push({x, y});

}

}

}