61 lines
1.5 KiB
C++
61 lines
1.5 KiB
C++
#include <functional>
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#include <iostream>
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#include <queue>
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#include <utility>
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#include <vector>
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/**
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* 1254. Number of Closed Islands
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*
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* Given a 2D grid consists of 0s (land) and 1s (water). An island is a maximal 4-directionally connected group of 0s and a closed island is an island totally (all left, top, right, bottom) surrounded by 1s.
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* Return the number of closed islands.
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*/
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class Solution {
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private:
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static const inline int dX[] = {0, 1, 0, -1}, dY[] = {1, 0, -1, 0};
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public:
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static int closedIsland(std::vector<std::vector<int>>&);
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};
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int Solution::closedIsland(std::vector<std::vector<int>>& G) {
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const int m = G.size(), n = G.front().size();
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auto setAs1 = [&](int x, int y) {
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if (G[x][y]) return 0;
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std::queue<std::pair<int, int>> q;
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q.emplace(x, y);
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for (int nx, ny; !q.empty(); q.pop()) {
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auto&& [cx, cy] = q.front();
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G[cx][cy] = 1;
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for (int i = 0; i < 4; ++i) {
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nx = cx + dX[i];
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ny = cy + dY[i];
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if (nx >= 0 && nx < m && ny >= 0 && ny < n && G[nx][ny] == 0)
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q.emplace(nx, ny);
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}
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}
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return 1;
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};
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for (int i = 0; i < n; ++i)
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setAs1(0, i), setAs1(m - 1, i);
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for (int i = 1; i < m; ++i)
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setAs1(i, 0), setAs1(i, n - 1);
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int ret = 0;
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for (int i = 1; i < m - 1; ++i)
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for (int j = 1; j < n - 1; ++j)
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ret += setAs1(i, j);
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return ret;
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}
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int main() {
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std::vector<std::vector<int>> a {
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{1,1,1,1,1,1,1,0},
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{1,0,0,0,0,1,1,0},
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{1,0,1,0,1,1,1,0},
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{1,0,0,0,0,1,0,1},
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{1,1,1,1,1,1,1,0}
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};
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std::cout << Solution::closedIsland(a);
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return 0;
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}
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