UVA.548 Tree(二叉树 DFS)

UVA.548 Tree(二叉树 DFS)

题意分析

给出一棵树的中序遍历和后序遍历，从所有叶子节点中找到一个使得其到根节点的权值最小。若有多个，输出叶子节点本身权值小的那个节点。

先递归建树，然后DFS求解。

代码总览

#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <string>
#include <sstream>
#include <queue>
#include <stack>
#include <set>
#include <map>
#include <vector>
#define nmax 100000
#define INF 0x3f3f3f3f
using namespace std;
int inorder[nmax],postorder[nmax];
int lnode[nmax],rnode[nmax];
int i;
bool read_input()
{
    memset(inorder,0,sizeof(inorder));
    memset(postorder,0,sizeof(postorder));
    string s;
    if(!getline(cin,s)) return false;
    else{
        stringstream ss(s);
        i = 0;
        int x;
        while(ss >> x) inorder[i++] = x;
        getline(cin,s);
        stringstream sss(s);
        i = 0;
        while(sss>>x) postorder[i++] = x;
    }
    return true;
}
// 递归建树
int buildtree(int l1,int r1, int l2, int r2)
{
    if(l1>r1) return 0;
    int root = postorder[r2];
    int p = l1;
    while(inorder[p] != root) p++;
    int cnt = p-l1;
    lnode[root] = buildtree(l1,p-1,l2,l2+cnt-1);
    rnode[root] = buildtree(p+1,r1,l2+cnt,r2-1);//
    return root;
}
int bestsum,best;
void dfs(int u, int sum)
{
    sum+=u;
    if(!lnode[u] && !rnode[u])
        if(sum<bestsum || (sum == bestsum && u<best)){
            best = u;
            bestsum = sum;
        }
    if(lnode[u]) dfs(lnode[u],sum);
    if(rnode[u]) dfs(rnode[u],sum);
}
int main()
{
    //freopen("in.txt","r",stdin);
    while(read_input()){
        bestsum = INF;best = INF;
        buildtree(0,i-1,0,i-1);
        dfs(postorder[i-1],0);
        cout<<best<<"\n";
    }
    return 0;
}