《程序员代码面试指南》第八章 数组和矩阵问题 打印N 个数组整体最大的Top K

题目

打印N 个数组整体最大的Top K

java代码

package com.lizhouwei.chapter8;

/**
 * @Description: 打印N 个数组整体最大的Top K
 * @Author: lizhouwei
 * @CreateDate: 2018/5/9 20:11
 * @Modify by:
 * @ModifyDate:
 */
public class Chapter8_20 {

    public void printTopK(int[][] matrix, int topK) {
        int heapSize = matrix.length;
        HeapNode[] heap = new HeapNode[heapSize];
        for (int i = 0; i < heapSize; i++) {
            int index = matrix[i].length - 1;
            heap[i] = new HeapNode(matrix[i][index], i, index);
            heapInsert(heap, i);
        }
        System.out.print("TOP" + topK + ": ");
        HeapNode node = null;
        for (int i = 0; i < topK; i++) {
            System.out.print(heap[0].value + " ");
            if (heap[0].index != 0) {
                heap[0].value = matrix[heap[0].arrNum][--heap[0].index];
            } else {
                swap(heap, 0, --heapSize);
            }
            heapify(heap, 0, heapSize);
        }
    }

    public void heapInsert(HeapNode[] heap, int index) {
        int parent = 0;
        while (index > 0) {
            parent = (index - 1) / 2;
            if (heap[parent].value < heap[index].value) {
                swap(heap, parent, index);
            } else {
                break;
            }
        }
    }

    public void heapify(HeapNode[] heap, int index, int heapSize) {
        int left = 2 * index + 1;
        int right = 2 * index + 2;
        int largest = index;
        while (left < heapSize) {
            if (heap[left].value > heap[index].value) {
                largest = left;
            }
            if (right < heapSize && heap[right].value > heap[largest].value) {
                largest = right;
            }
            if (largest == index) {
                break;
            }
            swap(heap, largest, index);
            index = largest;
            left = 2 * index + 1;
            right = 2 * index + 2;
        }
    }

    public void swap(HeapNode[] heap, int a, int b) {
        HeapNode temp = heap[a];
        heap[a] = heap[b];
        heap[b] = temp;
    }
}

class HeapNode {
    public int value;
    public int arrNum;
    public int index;

    public HeapNode(int value, int arrNum, int index) {
        this.value = value;
        this.arrNum = arrNum;
        this.index = index;
    }

    //测试
    public static void main(String[] args) {
        Chapter8_20 chapter = new Chapter8_20();
        int[][] arr = {{219, 405, 538, 845, 971}, {148, 558}, {52, 99, 348, 691}};
        chapter.printTopK(arr, 5);
    }
}

结果