題目

最小堆實現

解答

public class MinHeap {

    public static void main(String[] args) {
        int[] test = {23,42,5,1,56};
        heapify(test);
        print(0,test);
    }


    public static void print(int index,int[] tests){

        System.out.println(tests[getLeft(index)]);
        System.out.println(tests[index]);
        System.out.println(tests[getRight(index)]);

    }
    /*
     * @param A: Given an integer array
     * @return: nothing
     */
 

    public static void heapify(int[] A) {
        // write your code here
        for (int i = A.length/2-1;i>=0; i--) {
            change(i, A.length, A);
        }
    }

    public static void change(int index, int length, int[] temp) {
        int smallest = index;
        int left = getLeft(index);
        int
 
 right = getRight(index);

        if (left < length && temp[left] < temp[smallest]) {
            smallest = left;
        }

        if (right < length && temp[right] < temp[smallest]) {
            smallest = right;
        }
        // 左右結點的值都大於根節點，直接return，不做任何操作
        if
 
 (index == smallest) {
            return;
        }
        swap(index, smallest, temp);
        change(smallest, length, temp);
    }

    public  static void swap(int index, int smallest, int[] temp) {
        int curr = temp[index];
        temp[index] = temp[smallest];
        temp[smallest] = curr;
    }

    public static int getLeft(int index) {
        return index * 2 + 1;
    }

    public  static int getRight(int index) {
        return index * 2 + 2;
    }
}