UVA548 Tree

版权声明：听说这里让写版权声明～～～ https://blog.csdn.net/m0_37691414/article/details/83548161

根据一棵树的中序遍历、后序遍历来构造这棵树，然后dfs或这bfs一遍这棵树，找出到叶子结点到根节点路径权和最小，如果有多解则叶子节点本身权值最小。

#include<cstdio>
#include<cstring>
#include<algorithm>
#include<iostream>
#include<sstream>
#include<string>
using namespace std;
const int maxn = 10000 + 10;
const int INF = 0x3f3f3f;
int in[maxn], post[maxn];
int lch[maxn], rch[maxn];
int n;
bool read(int *a){
	string line;
	if(!getline(cin, line)) return false;
	stringstream ss(line);
	int x; 
	n = 0;
	while(ss >> x) a[n++] = x;
	return n > 0;
}
int build(int L1, int R1, int L2, int R2){
	if(L1 > R1) return 0;
	int root = post[R2];
	int p = L1;
	while(in[p] != root) ++p;
	int cnt = p - L1;
	lch[root] = build(L1, p - 1, L2, L2 + cnt - 1);
	rch[root] = build(p + 1, R1, L2 + cnt, R2 - 1);
	return root;
}
int best, bestSum;
void dfs(int u, int sum){
	sum += u;
	if(!lch[u] && !rch[u]) {
		if(sum < bestSum || (sum == bestSum && u < best)){
			best = u; bestSum = sum;
		}
	}
	if(lch[u]) dfs(lch[u], sum);
	if(rch[u]) dfs(rch[u], sum);
}
int main(){
	//freopen("data.in", "r", stdin);
	while(read(in)){
		read(post);
		build(0, n - 1, 0, n - 1);
		bestSum = INF;
		dfs(post[n - 1], 0);
		printf("%d\n", best);
	}
	return 0;
}