牛客NC357 矩阵第K小【中等堆 Java、Go、PHP】-编程知识

题目

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题目链接：
https://www.nowcoder.com/practice/c754e7a920614cba9b8b692ba9b20b5d

核心

堆，或者叫优先级队列

参考答案Java

import java.util.*;public class Solution {/*** 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可*** @param matrix int整型ArrayList<ArrayList<>>* @param k int整型* @return int整型*/public int KthinMatrix (ArrayList<ArrayList<Integer>> matrix, int k) {//优先级队列int n = matrix.size(); //行和列都是nboolean[][] visited = new boolean[n][n];PriorityQueue<int[]> pq = new PriorityQueue<>(new Comparator<int[]>() {public int compare(int[] a,int[] b) { //int[]:0:横坐标x  1：纵坐标y  2：xy对应的位置值return matrix.get(a[0]).get(a[1]) - matrix.get(b[0]).get(b[1]);}});int[] root = {0, 0, matrix.get(0).get(0)};visited[0][0] = true;pq.add(root);for (int i = 0; i < k - 1 ; i++) {int[] cur = pq.poll();int x = cur[0];int y = cur[1];if (x < n && y + 1 < matrix.get(x).size() && !visited[x][y + 1]) {visited[x][y + 1] = true;pq.add(new int[] {x, y + 1, matrix.get(x).get(y + 1)});}if (x + 1 < n && y < matrix.get(x).size() && !visited[x + 1][y]) {visited[x + 1][y] = true;pq.add(new int[] {x + 1, y, matrix.get(x + 1).get(y)});}}return pq.poll()[2];}}

参考答案Go

package main/*** 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可*** @param matrix int整型二维数组* @param k int整型* @return int整型*/
func KthinMatrix(matrix [][]int, k int) int {//优先级队列，堆n := len(matrix)visited := make([][]bool, n)for i := 0; i < n; i++ {visited[i] = make([]bool, n)}pq := &MyPQ{make([]PQNode, 10), 0, 10}pq.add(0, 0, matrix[0][0])visited[0][0] = truefor i := 0; i < k-1; i++ {poll := pq.poll()x := poll.xy := poll.yif x < n && y+1 < n && !visited[x][y+1] { //题目说了矩阵n*npq.add(x, y+1, matrix[x][y+1])visited[x][y+1] = true}if x+1 < n && y < n && !visited[x+1][y] {pq.add(x+1, y, matrix[x+1][y])visited[x+1][y] = true}}return pq.poll().data
}// 本答案用小顶堆，从上往下递增
type PQNode struct {x    int //横坐标y    int //纵坐标data int //坐标值
}
type MyPQ struct {arr         []PQNodesize        intdefaultSize int
}func (pq *MyPQ) ensureCap(cap int) { //堆的扩容curlen := len(pq.arr)if curlen >= cap {return}newlen := curlen + curlen>>1newarr := make([]PQNode, newlen)for i := 0; i < curlen; i++ {newarr[i] = pq.arr[i]}pq.arr = newarr
}func (pq *MyPQ) add(x, y, data int) {pq.ensureCap(pq.size + 1)node := PQNode{x, y, data}pq.arr[pq.size] = nodepq.shiftup(pq.size)pq.size++}// 上滤
func (pq *MyPQ) shiftup(idx int) {root := pq.arr[idx]for idx > 0 {pidx := (idx - 1) >> 1pdata := pq.arr[pidx]if pdata.data < root.data {break}pq.arr[idx] = pdataidx = pidx}pq.arr[idx] = root
}// 获取并删除堆顶元素，然后下窜，整理堆
func (pq *MyPQ) poll() PQNode {root := pq.arr[0]//fmt.Println("root:", root.data)pq.arr[0] = pq.arr[pq.size-1]pq.size -= 1pq.shiftdown(0)return root
}func (pq *MyPQ) shiftdown(idx int) {root := pq.arr[idx]half := pq.size >> 1 //核心1: 用位移，别用除法for idx < half {childidx := (idx << 1) + 1 //核心2: 用位移，别用乘法rightidx := childidx + 1child := pq.arr[childidx]//小顶堆，哪个子节点更小，哪边就上去if rightidx < pq.size && pq.arr[childidx].data > pq.arr[rightidx].data {childidx = rightidxchild = pq.arr[rightidx]}if child.data >= root.data {break}pq.arr[idx] = childidx = childidx}pq.arr[idx] = root
}

参考答案PHP

<?php/*** 代码中的类名、方法名、参数名已经指定，请勿修改，直接返回方法规定的值即可** * @param matrix int整型二维数组 * @param k int整型 * @return int整型*/
function KthinMatrix( $matrix ,  $k )
{// 堆，优先级队列$pq = new PQ();$n =count($matrix);$visited = [];for($i=0;$i<$n;$i++){for($j=0;$j<$n;$j++){$visited[$i][$j] =false;}}$pq->add(0,0,$matrix[0][0]);$visited[0][0]= true;for($i=0;$i<$k-1;$i++){$poll = $pq->poll();$x = $poll[0];$y = $poll[1];if($x <$n && $y+1<$n && !$visited[$x][$y+1]){$pq->add($x,$y+1,$matrix[$x][$y+1]);$visited[$x][$y+1]=true;}if($x+1<$n&&$y<$n && !$visited[$x+1][$y]){$pq->add($x+1,$y,$matrix[$x+1][$y]);$visited[$x+1][$y]=true;}}return $pq->poll()[2];
}//本答案用对，小顶对，也就是从上往下是递增的
class PQ{public $arr=[]; //二维数组，0：横坐标 1：纵坐标  2：坐标值public $defaultsize =10;public $size;public function __construct(){$this->size =0;for($i=0;$i<$this->defaultsize;$i++){$this->arr[$i] =[];}}public function ensurecap($cap){$curlen =count($this->arr);if($curlen >= $cap){return;}$newlen = $curlen+$curlen>>1;$newarr = [];for($i=0;$i<$newlen;$i++){if($i<$curlen){$newarr[$i] = $this->arr[$i];}else{$newarr[$i] =[];}}$this->arr = $newarr;}public function  add($x,$y,$data){$this->ensurecap($this->size+1);$this->arr[$this->size] = [$x,$y,$data];$this->shiftup($this->size);$this->size++;}//上滤public function shiftup($idx){$root = $this->arr[$idx];while ($idx>0){$pidx = ($idx-1) >>1;$parent= $this->arr[$pidx];if($parent[2] <=$root[2]){ //当前节点比父节点大，退出break;}$this->arr[$idx] = $parent;$idx = $pidx;}$this->arr[$idx] = $root;}public function poll() {$root = $this->arr[0];$this->arr[0] = $this->arr[$this->size-1];$this->size-=1;$this->shiftdown(0);return $root;}//下窜public function shiftdown($idx){$root = $this->arr[$idx];$half = $this->size >>1;while ($idx<$half){$childidx = ($idx << 1)+1;$rightidx = $childidx+1;$child = $this->arr[$childidx];if($rightidx<$this->size && $child[2] > $this->arr[$rightidx][2]){$childidx = $rightidx;$child = $this->arr[$rightidx];}if($child[2] >=$root[2]){break;}$this->arr[$idx] = $child;$idx =$childidx;}$this->arr[$idx] = $root;}
}