第六章部分例题

#include <iostream>
#include <sstream>

using namespace std;

const int maxn=100000;
int n;
int postorder[maxn],inorder[maxn];
int lh[maxn],rh[maxn];


bool read_list(int* a)
{
    string line;

    if(!getline(cin,line)) return false;
                                /*利用stringstream来构造字符串流读入一行数据*/
    stringstream ss(line);

    n=0;
    int num;
    while(ss>>num) a[n++]=num;

    return n>0;
}

int built_tree(int l1,int r1,int l2,int r2)
{                              /*递归建立二叉树返回数根,用各个节点的值来标志*/
    if(l1>r1) return 0;

    int root=postorder[r2];

    int p=l1;

    while(inorder[p]!=root) p++;

    int cnt=p-l1;

    lh[root]=built_tree(l1,p-1,l2,l2+cnt-1);
    rh[root]=built_tree(p+1,r1,l2+cnt,r2-1);

    return root;
}

int best_sum,best;

void dfs(int u,int sum)
{                             /*深度优先,如果是叶子节点就进行判断*/
    sum+=u;

    if(!lh[u] && !rh[u])
    {
        if(sum<best_sum || (sum==best_sum && u<best))
        {
            best_sum=sum;
            best=u;
        }
    }

    if(lh[u]) dfs(lh[u],sum);
    if(rh[u]) dfs(rh[u],sum);
}


int main()
{

    while(read_list(inorder))
    {
        read_list(postorder);
        built_tree(0,n-1,0,n-1);

        int u=0,sum=0;

        best=u;
        best_sum=100000000;

        dfs(postorder[n-1],sum);

        cout<<best<<endl;
    }

    return 0;
}