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package class18;
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// 本题测试链接 : https://leetcode.com/problems/shortest-bridge/
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public class Code02_ShortestBridge {
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public static int shortestBridge(int[][] m) {
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int N = m.length;
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int M = m[0].length;
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int all = N * M;
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int island = 0;
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int[] curs = new int[all];
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int[] nexts = new int[all];
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int[][] records = new int[2][all];
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for (int i = 0; i < N; i++) {
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for (int j = 0; j < M; j++) {
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if (m[i][j] == 1) { // 当前位置发现了1！
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// 把这一片的1，都变成2，同时，抓上来了，这一片1组成的初始队列
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// curs, 把这一片的1到自己的距离，都设置成1了，records
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int queueSize = infect(m, i, j, N, M, curs, 0, records[island]);
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int V = 1;
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while (queueSize != 0) {
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V++;
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// curs里面的点，上下左右，records[点]==0， nexts
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queueSize = bfs(N, M, all, V, curs, queueSize, nexts, records[island]);
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int[] tmp = curs;
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curs = nexts;
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nexts = tmp;
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}
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island++;
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}
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}
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}
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int min = Integer.MAX_VALUE;
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for (int i = 0; i < all; i++) {
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min = Math.min(min, records[0][i] + records[1][i]);
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}
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return min - 3;
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}
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// 当前来到m[i][j] , 总行数是N，总列数是M
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// m[i][j]感染出去(找到这一片岛所有的1),把每一个1的坐标，放入到int[] curs队列！
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// 1 (a,b) -> curs[index++] = (a * M + b)
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// 1 (c,d) -> curs[index++] = (c * M + d)
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// 二维已经变成一维了， 1 (a,b) -> a * M + b
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// 设置距离record[a * M +b ] = 1
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public static int infect(int[][] m, int i, int j, int N, int M, int[] curs, int index, int[] record) {
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if (i < 0 || i == N || j < 0 || j == M || m[i][j] != 1) {
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return index;
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}
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// m[i][j] 不越界，且m[i][j] == 1
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m[i][j] = 2;
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int p = i * M + j;
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record[p] = 1;
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// 收集到不同的1
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curs[index++] = p;
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index = infect(m, i - 1, j, N, M, curs, index, record);
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index = infect(m, i + 1, j, N, M, curs, index, record);
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index = infect(m, i, j - 1, N, M, curs, index, record);
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index = infect(m, i, j + 1, N, M, curs, index, record);
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return index;
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}
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// 二维原始矩阵中，N总行数，M总列数
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// all 总 all = N * M
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// V 要生成的是第几层 curs V-1 nexts V
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// record里面拿距离
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public static int bfs(int N, int M, int all, int V,
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int[] curs, int size, int[] nexts, int[] record) {
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int nexti = 0; // 我要生成的下一层队列成长到哪了？
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for (int i = 0; i < size; i++) {
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// curs[i] -> 一个位置
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int up = curs[i] < M ? -1 : curs[i] - M;
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int down = curs[i] + M >= all ? -1 : curs[i] + M;
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int left = curs[i] % M == 0 ? -1 : curs[i] - 1;
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int right = curs[i] % M == M - 1 ? -1 : curs[i] + 1;
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if (up != -1 && record[up] == 0) {
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record[up] = V;
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nexts[nexti++] = up;
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}
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if (down != -1 && record[down] == 0) {
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record[down] = V;
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nexts[nexti++] = down;
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}
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if (left != -1 && record[left] == 0) {
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record[left] = V;
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nexts[nexti++] = left;
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}
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if (right != -1 && record[right] == 0) {
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record[right] = V;
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nexts[nexti++] = right;
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}
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}
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return nexti;
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}
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}
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