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codeforces 712B B. Memory and Trident(水题)
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题目链接：
B. Memory and Trident
time limit per test
2 seconds
memory limit per test
256 megabytes
input
standard input
output
standard output
Memory is performing a walk on the two-dimensional plane, starting at the origin. He is given a string s with his directions for motion:
- An 'L' indicates he should move one unit left.
- An 'R' indicates he should move one unit right.
- A 'U' indicates he should move one unit up.
- A 'D' indicates he should move one unit down.
But now Memory wants to end at the origin. To do this, he has a special trident. This trident can replace any character in s with any of 'L', 'R', 'U', or 'D'. However, because he doesn't want to wear out the trident, he wants to make the minimum number of edits possible. Please tell Memory what is the minimum number of changes he needs to make to produce a string that, when walked, will end at the origin, or if there is no such string.
Input
The first and only line contains the string s (1 ≤ |s| ≤ 100 000) — the instructions Memory is given.
Output
If there is a string satisfying the conditions, output a single integer — the minimum number of edits required. In case it's not possible to change the sequence in such a way that it will bring Memory to to the origin, output -1.
Examples
input
RRU
output
-1
input
UDUR
output
1
input
RUUR
output
2题意：问最少改变多少个才能最后回到原点;思路：水水水;AC代码：
#include <iostream>
#include <cstdio>
#include <cstring>
#include <algorithm>
#include <cmath>
#include <bits/stdc++.h>
#include <stack>
#include <map>using namespace std;#define For(i,j,n) for(int i=j;i<=n;i++)
#define mst(ss,b) memset(ss,b,sizeof(ss));typedef long long LL;template<class T> void read(T&num) {
char CH; bool F=false;
for(CH=getchar();CH<'0'||CH>'9';F= CH=='-',CH=getchar());
for(num=0;CH>='0'&&CH<='9';num=num*10+CH-'0',CH=getchar());
F && (num=-num);
}
int stk[70], tp;
template<class T> inline void print(T p) {
if(!p) { puts("0"); return; }
while(p) stk[++ tp] = p%10, p/=10;
while(tp) putchar(stk[tp--] + '0');
putchar('\n');
}const int mod=1e9+7;
const double PI=acos(-1.0);
const LL inf=1e18;
const int N=(1<<20)+10;
const int maxn=1e5+110;
const double eps=1e-12;char s[maxn];
int main()
{
scanf("%s",s);
int len=strlen(s),l=0,r=0,u=0,d=0;
for(int i=0;i<len;i++)
{
if(s[i]=='R')r++;
else if(s[i]=='L')l++;
else if(s[i]=='U')u++;
else d++;
}
if(len&1)cout<<"-1\n";
else cout<<(abs(l-r)+abs(u-d))/2<<endl;
return 0;
}
