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Commitc6b98a1

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‎README.md

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|678|[Valid Parenthesis String](https://leetcode.com/problems/valid-parenthesis-string/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_678.java) | O(n) | O(1) | Medium| Recursion, Greedy
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|677|[Map Sum Pairs](https://leetcode.com/problems/map-sum-pairs/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_677.java) | O(n) | O(n) | Medium | HashMap
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|676|[Implement Magic Dictionary](https://leetcode.com/problems/implement-magic-dictionary/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_676.java)| O(n^2)| O(n)| Medium|
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|675|[Cut Off Trees for Golf Event](https://leetcode.com/problems/cut-off-trees-for-golf-event/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_675.java) | O((m*n)^2) | O(m*n) | Hard | BFS
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|674|[Longest Continuous Increasing Subsequence](https://leetcode.com/problems/longest-continuous-increasing-subsequence/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_674.java)| O(n^2)| O(1)| Easy|
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|672|[Bulb Switcher II](https://leetcode.com/problems/bulb-switcher-ii/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_672.java) | O(1) | O(1) | Medium | Math
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|671|[Second Minimum Node In a Binary Tree](https://leetcode.com/problems/second-minimum-node-in-a-binary-tree/)|[Solution](../master/src/main/java/com/fishercoder/solutions/_671.java) | O(n) | O(n) | Easy | Tree, DFS
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packagecom.fishercoder.solutions;
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importjava.util.LinkedList;
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importjava.util.List;
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importjava.util.PriorityQueue;
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importjava.util.Queue;
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/**
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* 675. Cut Off Trees for Golf Event
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*
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* You are asked to cut off trees in a forest for a golf event.
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* The forest is represented as a non-negative 2D map, in this map:
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* 0 represents the obstacle can't be reached.
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* 1 represents the ground can be walked through.
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*
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* The place with number bigger than 1 represents a tree can be walked through,
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* and this positive number represents the tree's height.
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*
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* You are asked to cut off all the trees in this forest in the order of tree's height -
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* always cut off the tree with lowest height first.
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* And after cutting, the original place has the tree will become a grass (value 1).
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*
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* You will start from the point (0, 0) and you should output the minimum steps you need to walk to cut off all the trees.
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*
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* If you can't cut off all the trees, output -1 in that situation.
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* You are guaranteed that no two trees have the same height and there is at least one tree needs to be cut off.
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*
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* Example 1:
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* Input:
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* [
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* [1,2,3],
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* [0,0,4],
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* [7,6,5]
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* ]
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* Output: 6
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*
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* Example 2:
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* Input:
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* [
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* [1,2,3],
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* [0,0,0],
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* [7,6,5]
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* ]
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* Output: -1
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*
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* Example 3:
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* Input:
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* [
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* [2,3,4],
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* [0,0,5],
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* [8,7,6]
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* ]
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* Output: 6
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*
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* Explanation: You started from the point (0,0) and you can cut off the tree in (0,0) directly without walking.
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* Hint: size of the given matrix will not exceed 50x50.
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*/
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publicclass_675 {
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publicstaticclassSolution1 {
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publicintcutOffTree(List<List<Integer>>forest) {
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if (forest ==null ||forest.isEmpty() ||forest.size() ==0 ||forest.get(0).get(0) ==0) {
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return -1;
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}
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intm =forest.size();
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intn =forest.get(0).size();
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/**cut trees in ascending order*/
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PriorityQueue<Tree>heap =newPriorityQueue<>((a,b) ->a.height -b.height);
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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 (forest.get(i).get(j) >1) {
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/**This is important: we'll add trees that are only taller than 1!!!*/
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heap.offer(newTree(i,j,forest.get(i).get(j)));
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}
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}
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}
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intsum =0;
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Treestart =newTree();
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while (!heap.isEmpty()) {
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Treecurr =heap.poll();
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intstep =bfs(forest,curr,start,m,n);
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if (step == -1) {
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return -1;
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}
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sum +=step;
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start =curr;
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}
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returnsum;
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}
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privateintbfs(List<List<Integer>>forest,Treetarget,Treestart,intm,intn) {
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int[]dirs =newint[]{0,1,0, -1,0};
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boolean[][]visited =newboolean[m][n];
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Queue<Tree>queue =newLinkedList<>();
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queue.offer(start);
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visited[start.x][start.y] =true;
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intstep =0;
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while (!queue.isEmpty()) {
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intsize =queue.size();
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for (intk =0;k <size;k++) {
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Treetree =queue.poll();
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if (tree.x ==target.x &&tree.y ==target.y) {
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returnstep;
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}
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for (inti =0;i <4;i++) {
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intnextX =tree.x +dirs[i];
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intnextY =tree.y +dirs[i +1];
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if (nextX <0 ||nextY <0 ||nextX >=m ||nextY >=n ||visited[nextX][nextY] ||forest.get(nextX).get(nextY) ==0) {
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continue;
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}
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queue.offer(newTree(nextX,nextY,forest.get(nextX).get(nextY)));
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visited[nextX][nextY] =true;
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}
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}
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step++;
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}
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return -1;
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}
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classTree {
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intx;
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inty;
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intheight;
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publicTree(intx,inty,intheight) {
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this.x =x;
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this.y =y;
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this.height =height;
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}
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publicTree() {
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this.x =0;
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this.y =0;
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this.height =0;
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}
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}
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}
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}
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packagecom.fishercoder;
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importcom.fishercoder.common.utils.ArrayUtils;
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importcom.fishercoder.solutions._675;
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importorg.junit.BeforeClass;
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importorg.junit.Test;
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importjava.util.ArrayList;
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importjava.util.Arrays;
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importjava.util.List;
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importstaticorg.junit.Assert.assertEquals;
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publicclass_675Test {
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privatestatic_675.Solution1solution1;
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privatestaticList<List<Integer>>forest;
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@BeforeClass
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publicstaticvoidsetup() {
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solution1 =new_675.Solution1();
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}
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@Test
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publicvoidtest1() {
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forest =newArrayList<>();
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forest.add(Arrays.asList(1,2,3));
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forest.add(Arrays.asList(0,0,4));
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forest.add(Arrays.asList(7,6,5));
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assertEquals(6,solution1.cutOffTree(forest));
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}
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@Test
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publicvoidtest2() {
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forest =newArrayList<>();
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forest.add(Arrays.asList(1,2,3));
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forest.add(Arrays.asList(0,0,0));
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forest.add(Arrays.asList(7,6,5));
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assertEquals(-1,solution1.cutOffTree(forest));
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}
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@Test
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publicvoidtest3() {
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forest =newArrayList<>();
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forest.add(Arrays.asList(2,3,4));
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forest.add(Arrays.asList(0,0,5));
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forest.add(Arrays.asList(8,7,6));
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assertEquals(6,solution1.cutOffTree(forest));
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}
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@Test
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publicvoidtest4() {
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forest =ArrayUtils.buildList(newint[][]{
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{2,3,4,9},
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{0,0,5,10},
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{8,7,6,12},
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});
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assertEquals(13,solution1.cutOffTree(forest));
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}
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@Test
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publicvoidtest5() {
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forest =ArrayUtils.buildList(newint[][]{
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{0,0,0,3528,2256,9394,3153},
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{8740,1758,6319,3400,4502,7475,6812},
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{0,0,3079,6312,0,0,0},
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{6828,0,0,0,0,0,8145},
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{6964,4631,0,0,0,4811,0},
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{0,0,0,0,9734,4696,4246},
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{3413,8887,0,4766,0,0,0},
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{7739,0,0,2920,0,5321,2250},
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{3032,0,3015,0,3269,8582,0}});
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assertEquals(-1,solution1.cutOffTree(forest));
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}
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@Test
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publicvoidtest6() {
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forest =ArrayUtils.buildList(newint[][]{
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{54581641,64080174,24346381,69107959},
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{86374198,61363882,68783324,79706116},
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{668150,92178815,89819108,94701471},
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{83920491,22724204,46281641,47531096},
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{89078499,18904913,25462145,60813308}
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});
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assertEquals(57,solution1.cutOffTree(forest));
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}
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}

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