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Commit24221e6

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number of islands using union find
1 parent120d72e commit24221e6

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packagemedium;
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/**
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* Created by fishercoder1534 on 9/30/16.
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*/
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//Inspired by this post: https://discuss.leetcode.com/topic/39980/1d-union-find-java-solution-easily-generalized-to-other-problems
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publicclassNumberOfIslandsUnionFind {
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classUnionFind{
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intcount;
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intm,n;
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int[]ids;
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publicUnionFind(char[][]grid){
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m =grid.length;
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n =grid[0].length;
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ids =newint[m*n];
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for(inti =0;i <m;i++){
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for(intj =0;j <n;j++){
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if(grid[i][j] =='1') {
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count++;
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ids[i*n+j] =i*n+j;
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}
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}
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}
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}
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publicvoidunion(inti,intj){
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intx =find(ids,i);
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inty =find(ids,j);
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if(x !=y) {//note: this is when x != y, only in this case, we should union these two nodes, which makes sense naturally.
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count--;
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ids[x] =y;
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}
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}
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publicintfind(int[]ids,inti){
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if(ids[i] ==i)returni;
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returnfind(ids,ids[i]);
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}
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}
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publicintnumIslands(char[][]grid) {
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if(grid ==null ||grid.length ==0 ||grid[0].length ==0)return0;
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int[]dirs =newint[]{0,1,0,-1,0};
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UnionFinduf =newUnionFind(grid);
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intm =grid.length,n =grid[0].length;
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for(inti =0;i <m;i++){
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for(intj =0;j <n;j++){
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if(grid[i][j] =='1'){
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for(intk =0;k <4;k++){
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intx =i+dirs[k];
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inty =j+dirs[k+1];
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if(x >=0 &&x <m &&y >=0 &&y <n &&grid[x][y] =='1'){
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intid1 =i*n+j;
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intid2 =x*n+y;
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uf.union(id1,id2);
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}
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}
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}
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}
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}
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returnuf.count;
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}
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}

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