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leetcode_java/src/main/java/LeetCodeJava/DFS/MaxAreaOfIsland.java
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| package LeetCodeJava.DFS; | ||
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| // https://leetcode.com/problems/max-area-of-island/ | ||
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| import java.util.Arrays; | ||
| import java.util.List; | ||
| import java.util.Stack; | ||
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| // | ||
| //class Point { | ||
| // int x; | ||
| // int y; | ||
| // | ||
| // Point(int x, int y) { | ||
| // this.x = x; | ||
| // this.y = y; | ||
| // } | ||
| //} | ||
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| public class MaxAreaOfIsland { | ||
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| // TODO : fix below | ||
| // int ans = 0; | ||
| // List<Point> toVisit = Arrays.asList(); | ||
| // List<List<Integer>> collected; | ||
| // | ||
| // // V0 | ||
| // public int maxAreaOfIsland(int[][] grid) { | ||
| // | ||
| // int len = grid.length; | ||
| // int width = grid[0].length; | ||
| // | ||
| // if (len == 0 && width == 0) { | ||
| // return 0; | ||
| // } | ||
| // | ||
| // // collect "1" points | ||
| // for (int i = 0; i < len; i++) { | ||
| // for (int j = 0; j < width; j++) { | ||
| // if (grid[i][j] == 1) { | ||
| // toVisit.add(new Point(j, i)); | ||
| // } | ||
| // } | ||
| // } | ||
| // | ||
| // // dfs | ||
| // for (Point point : toVisit) { | ||
| // int tmp = this._help(grid, point.y, point.x, Arrays.asList()); | ||
| // this.ans = Math.max(this.ans, tmp); | ||
| // } | ||
| // return this.ans; | ||
| // } | ||
| // | ||
| // private int _help(int[][] grid, int x, int y, List<Integer> tmp) { | ||
| // | ||
| // int len = grid.length; | ||
| // int width = grid[0].length; | ||
| // | ||
| // if (grid[y][x] != 1) { | ||
| // return 0; | ||
| // } | ||
| // | ||
| // if (x >= width || y >= len) { | ||
| // return 0; | ||
| // } | ||
| // | ||
| // // mark as visit | ||
| // grid[y][x] = -1; | ||
| // // double check?? | ||
| // tmp.add(1); | ||
| // _help(grid, x + 1, y, tmp); | ||
| // _help(grid, x - 1, y, tmp); | ||
| // _help(grid, x, y + 1, tmp); | ||
| // _help(grid, x, y - 1, tmp); | ||
| // | ||
| // return tmp.size(); | ||
| // } | ||
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| // V1 | ||
| // IDEA : DFS (recursive) | ||
| // https://leetcode.com/problems/max-area-of-island/editorial/ | ||
| int[][] grid; | ||
| boolean[][] seen; | ||
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| public int area(int r, int c) { | ||
| if (r < 0 || r >= grid.length || c < 0 || c >= grid[0].length || | ||
| seen[r][c] || grid[r][c] == 0) | ||
| return 0; | ||
| seen[r][c] = true; | ||
| return (1 + area(r+1, c) + area(r-1, c) | ||
| + area(r, c-1) + area(r, c+1)); | ||
| } | ||
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| public int maxAreaOfIsland_1(int[][] grid) { | ||
| this.grid = grid; | ||
| seen = new boolean[grid.length][grid[0].length]; | ||
| int ans = 0; | ||
| for (int r = 0; r < grid.length; r++) { | ||
| for (int c = 0; c < grid[0].length; c++) { | ||
| ans = Math.max(ans, area(r, c)); | ||
| } | ||
| } | ||
| return ans; | ||
| } | ||
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| // V2 | ||
| // IDEA : DFS (iterative) | ||
| // https://leetcode.com/problems/max-area-of-island/editorial/ | ||
| public int maxAreaOfIsland_2(int[][] grid) { | ||
| boolean[][] seen = new boolean[grid.length][grid[0].length]; | ||
| int[] dr = new int[]{1, -1, 0, 0}; | ||
| int[] dc = new int[]{0, 0, 1, -1}; | ||
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| int ans = 0; | ||
| for (int r0 = 0; r0 < grid.length; r0++) { | ||
| for (int c0 = 0; c0 < grid[0].length; c0++) { | ||
| if (grid[r0][c0] == 1 && !seen[r0][c0]) { | ||
| int shape = 0; | ||
| Stack<int[]> stack = new Stack(); | ||
| stack.push(new int[]{r0, c0}); | ||
| seen[r0][c0] = true; | ||
| while (!stack.empty()) { | ||
| int[] node = stack.pop(); | ||
| int r = node[0], c = node[1]; | ||
| shape++; | ||
| for (int k = 0; k < 4; k++) { | ||
| int nr = r + dr[k]; | ||
| int nc = c + dc[k]; | ||
| if (0 <= nr && nr < grid.length && | ||
| 0 <= nc && nc < grid[0].length && | ||
| grid[nr][nc] == 1 && !seen[nr][nc]) { | ||
| stack.push(new int[]{nr, nc}); | ||
| seen[nr][nc] = true; | ||
| } | ||
| } | ||
| } | ||
| ans = Math.max(ans, shape); | ||
| } | ||
| } | ||
| } | ||
| return ans; | ||
| } | ||
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| } |