多路归并排序

没写过失败树，用它来实现下多路归并排序

测试数据：

4
4 43 545 21 44
6 1 4 8 2 6 0
4 1 -1 3 -6
7 8 1 -5 -6 5 -11 33

第一行代表是几路

后面一共4行，每行第一个数表示这行后面一共有多少个数字

对每行数据先快排，然后用失败树进行多路归并

#include <iostream>#include <vector>#include <cstdio>#include <algorithm>using namespace std;struct node{    int num, val;};struct contrast{    bool operator() (const node &a,const node &b)    {        return a.val < b.val;    }} cmp;vector<vector<node> > record;int main(){        int k;    scanf("%d", &k);    int total = 2 * k - 1;    vector<node> tree(total + 1);    vector<int> index(total + 1);    for(int i = 0; i <= total; i++)        index[i] = i;    vector<vector<node>::iterator> head(k);    for(int i = 0; i < k; i++)    {        int num;        scanf("%d", &num);        vector<node> v;        for(int j = 0; j < num; j++)        {            node data;            data.num = i;            scanf("%d", &data.val);            v.push_back(data);        }        sort(v.begin(), v.end(), cmp);        record.push_back(v);            }    for(int i = 0; i < k; i++)        head[i] = record[i].begin();    int tot = k;    for(int i = 0; i < k; i++)    {        tree[total - k + i + 1].val = head[i]->val;        tree[total - k + i + 1].num = head[i]->num;        head[i]++;        if(head[i] == record[i].end())            tot--;    }    while(true)    {        if(tot == 0)            break;        for(int ed = total / 2; ed > 0; ed--)        {            int left = ed * 2, right = ed * 2 + 1;            if(tree[left].val < tree[right].val)            {                tree[ed].val = tree[left].val;                tree[ed].num = tree[left].num;                index[ed] = index[left];            }            else            {                tree[ed].val = tree[right].val;                tree[ed].num = tree[right].num;                index[ed] = index[right];            }        }        printf("%d ", tree[1].val);        if(head[tree[1].num] == record[tree[1].num].end())        {            tot--;            tree[index[1]].num = -1;            tree[index[1]].val = INT_MAX;        }        else        {            tree[index[1]].val = head[tree[1].num]->val;            tree[index[1]].num = head[tree[1].num]->num;            head[tree[1].num]++;        }    }    printf("\n");        return 0;}

输出结果：

-11 -6 -6 -5 -1 0 1 1 1 2 3 4 5 6 8 8 21 33 43 44 545 

有个问题是我在

record.push_back(v);后面加head[i] = record[i].begin();让它每次循环的时候head指向每个数据段的头，但是这样程序有错，head感觉指向错误了，不知什么原因
要在这个循环外面给每个head赋值才成....不知道是为什么。。。谁能帮忙解答下