PAT：堆模板

Posted 2021-09-24 花落，莫相离

//注意为方便操作，堆的下标从1开始
const int maxn = 100;
int heap[maxn], n = 10;

//向下调整
void downAdjust(int low, int high){
    int i = low, j = 2*i;
    while(j <= high){
        if(j + 1 <= high && heap[j+1] > heap[j]){//此处不要忘记判断j+1是否超过了high
            j = j+1;
        }
        if(heap[i] < heap[j]){
            swap(heap[i], heap[j]);
            i = j;
            j = 2*i;
        }else{
            break;
        }
    }
}

//建堆
void createHeap(){
    for(int i = n/2; i >= 1; i--){
        downAdjust(i, n);
    }
}

//删除堆顶元素
void delTop(){
    heap[1] = heap[n--];
    downAdjust(1, n);   //此处后面的是n，因为n已经自减了
}

//向上调整
void upAdjust(int low, int high){
    int i = high, j = i/2;
    while(j >= low){
        if(heap[i] > heap[j]){
            swap(heap[i], heap[j]);
            i = j;
            j = i/2;
        }else{
            break;
        }
    }
}

//添加元素
void insert(int x){
    heap[++n] = x;
    upAdjust(1, n);
}

//堆排序
void heapSort(){
    createHeap();
    for(int i = n; i > 1; i--){//从后往前倒着枚举交换
        swap(heap[1], heap[i]);
        downAdjust(1, i-1);
    }
}