poj-3253 Fence Repair **

/*
 * 3253 Fence Repair.cpp
 *
 *  Created on: 2011-10-25
 *
 *    Huffman + 堆排
 *
 *   _int64 让我WA了无数次， 郁闷
 *
 */

#include <iostream>
using namespace std;

const int maxn = 50000 + 5;
__int64 len[maxn], n, size;

inline int left(int i){
    return 2 * i + 1;
}
inline int right(int i){
    return 2 * i + 2;
}
inline int parent(int i){
    if(i == 0) return -1;
    return (i-1)/2;
}

void minHeapify(int x){
    int y = left(x);
    int tmp = len[x];
    while(y < size){
        if(y < size-1 && len[y+1] < len[y])
            y = y+1;
        if(len[y] >= tmp)
            break;
        len[x] = len[y];
        x = y;
        y = left(x);
    }
    len[x] = tmp;
}

void makeHeap(){
    for(int i=size/2-1; i>=0; i--)
        minHeapify(i);
}

int extractMin(){
    if(size == 0) return -1;

    int tmp = len[0];
    len[0] = len[--size];
    minHeapify(0);

    return tmp;
}

void insert(int key){
    int pos = size++;
    while(parent(pos) >= 0 && len[parent(pos)] > key){
        len[pos] = len[parent(pos)];
        pos = parent(pos);
    }
    len[pos] = key;
}



void buildHuffman(){
    __int64 a, b, c, sum = 0;

    while(size >= 2){
        a = extractMin();
        b = extractMin();

        c = (a + b);
        sum += c;

        insert(c);
    }

    cout << sum << endl;
}


int main(){
    while(cin >> n){
        for(int i=0; i<n; i++)
            cin >> len[i];
        size = n;

        if(n == 1){
            cout << 0 << endl;
            continue;
        }

        makeHeap();

        buildHuffman();
    }

    return 0;
}