大意:给定前序和后序遍历,先找出从根到叶sum最小的路径,然后输出叶子上的值,如果有多条路径满足,输出值最小的。
做法:
算法入门经典p106有详细介绍,当然根据是否建树,也有两种做法:
做法一:
#include<iostream> #include<cstdio> #include<cstring> #include<cctype> #include<cstdlib> using namespace std; char s[100005]; int v1[100005],v2[100005],top; int min_sum,ans; int init(char *s,int *v) { int top=0; for(int i=0;s[i];i++) { while(s[i]==' ') i++; v[top]=0; while(s[i]&&isdigit(s[i])) { v[top]=v[top]*10+s[i]-'0'; i++; } top++; if(!s[i]) break; } return top; } int find(int *v,int n,int c) { for(int i=n-1;i>=0;i--) if(v[i]==c) return i; return 0; } void build(int n,int *v1,int *v2,int sum) { if(n<=0) return ; int p=find(v1,n,v2[n-1]); sum+=v2[n-1]; if(p<=0&&n-p-1<=0) { if(sum==min_sum) ans=min(ans,v2[n-1]); else if(sum<min_sum) { min_sum=sum; ans=v2[n-1]; } return ; } build(p,v1,v2,sum); build(n-p-1,v1+p+1,v2+p,sum); } int main() { while(gets(s)) { int v; init(s,v1); gets(s); top=init(s,v2); ans=min_sum=10000000; build(top,v1,v2,0); printf("%d\n",ans); } return 0; }
做法二:
#include<iostream>
#include<cstdio>
#include<cstring>
#include<cctype>
#include<cstdlib>
using namespace std;
struct node
{
struct node *left;
struct node *right;
int v;
};
node *root;
char s[100005];
int v1[100005],v2[100005],top;
int init(char *s,int *v)
{
int top=0;
for(int i=0;s[i];i++)
{
while(s[i]=='')
i++;
v[top]=0;
while(s[i]&&isdigit(s[i]))
{
v[top]=v[top]*10+s[i]-'0';
i++;
}
top++;
if(!s[i]) break;
}
return top;
}
int find(int *v,int n,int c)
{
for(int i=n-1;i>=0;i--)
if(v[i]==c)
return i;
return 0;
}
node *build(int n,int *v1,int *v2)
{
if(n<=0)
return NULL;
int p=find(v1,n,v2[n-1]);
node *root=(node *)malloc(sizeof(node));
root->v=v2[n-1];
root->left=build(p,v1,v2);
root->right=build(n-p-1,v1+p+1,v2+p);
return root;
}
int min_sum,ans;
void dfs(node *root,int sum)
{
if(root==NULL)
return ;
sum+=root->v;
if(root->left==NULL&&root->right==NULL)
{
if(min_sum>sum)
{
min_sum=sum;
ans=root->v;
}
else if(min_sum==sum)
ans=min(ans,root->v);
return;
}
dfs(root->left,sum);
dfs(root->right,sum);
}
int main()
{
while(gets(s))
{
int v;
init(s,v1);
gets(s);
top=init(s,v2);
node *root;
root=build(top,v1,v2);
ans=min_sum=10000000;
dfs(root,0);
printf("%d\n",ans);
}
return 0;
}