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// 827. Making A Large Island
#include "leetcode.h"
/*
* you are given an 'm x n' binary matrix 'grid'. you are allowed to change at
* most one 0 to be 1. return size of the largest island in 'grid' after
* applying this operation. an island is a 4-directionally connected group of
* 1's.
*/
enum state { water, land };
struct point {
int r;
int c;
};
int explor_island(int r, int c, int id, int **grid, int nrow, int ncol) {
int land_size = 0, dir[4][2] = {{-1, 0}, {0, 1}, {1, 0}, {0, -1}};
struct point queue[nrow * ncol];
int front = 0, rear = 0;
queue[rear++] = (struct point){r, c};
grid[r][c] = id;
while (front < rear) {
struct point p = queue[front++];
++land_size;
for (int i = 0; i < 4; ++i) {
int dr = p.r + dir[i][0];
int dc = p.c + dir[i][1];
if (dr < 0 || dr >= nrow || dc < 0 || dc >= ncol || grid[dr][dc] != land)
continue;
grid[dr][dc] = id;
queue[rear++] = (struct point){dr, dc};
}
}
return land_size;
}
int largestIsland(int **grid, int gridSize, int *gridColSize) {
int max_island = gridSize * (*gridColSize), id = 2;
int *islands = (int *)calloc(max_island + 2, sizeof(int));
for (int i = 0; i < gridSize; ++i)
for (int j = 0; j < (*gridColSize); ++j)
if (grid[i][j] == land) {
islands[id] = explor_island(i, j, id, grid, gridSize, *gridColSize);
++id;
}
if (id == 2) {
free(islands);
return 1;
}
if (id == 3) {
int total = gridSize * (*gridColSize), land_size = islands[2] + 1;
int num_land = fmin(total, land_size);
free(islands);
return num_land;
}
int max_size = 1, dir[4][2] = {{-1, 0}, {0, 1}, {1, 0}, {0, -1}};
for (int i = 0; i < gridSize; ++i)
for (int j = 0; j < (*gridColSize); ++j) {
if (grid[i][j] != water)
continue;
bool vis[id];
int curr_size = 1;
memset(vis, 0, sizeof(vis));
for (int k = 0; k < 4; ++k) {
int dr = i + dir[k][0];
int dc = j + dir[k][1];
if (dr < 0 || dr >= gridSize || dc < 0 || dc >= (*gridColSize) ||
grid[dr][dc] <= land)
continue;
int curr_id = grid[dr][dc];
if (!vis[curr_id]) {
curr_size += islands[curr_id];
vis[curr_id] = true;
}
}
max_size = fmax(max_size, curr_size);
}
free(islands);
return max_size;
}
int main() {
int g1i[2][2] = {{1, 0}, {0, 1}}, g2i[2][2] = {{1, 1}, {1, 0}},
g3i[2][2] = {{1, 1}, {1, 1}};
struct two_d_arr g1, g2, g3;
two_d_arr_init(&g1, ARRAY_SIZE(g1i), ARRAY_SIZE(g1i[0]), g1i);
two_d_arr_init(&g2, ARRAY_SIZE(g2i), ARRAY_SIZE(g2i[0]), g2i);
two_d_arr_init(&g3, ARRAY_SIZE(g3i), ARRAY_SIZE(g3i[0]), g3i);
printf("%d\n", largestIsland(g1.arr, g1.row_size, g1.col_size)); // expect: 3
printf("%d\n", largestIsland(g2.arr, g2.row_size, g2.col_size)); // expect: 4
printf("%d\n", largestIsland(g3.arr, g3.row_size, g3.col_size)); // expect: 4
two_d_arr_free(&g1);
two_d_arr_free(&g2);
two_d_arr_free(&g3);
}
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