1038 Recover the Smallest Number（贪心，排序）

1038 Recover the Smallest Number（贪心）

0、题目

Given a collection of number segments, you are supposed to recover the smallest number from them. For example, given { 32, 321, 3214, 0229, 87 }, we can recover many numbers such like 32-321-3214-0229-87 or 0229-32-87-321-3214 with respect to different orders of combinations of these segments, and the smallest number is 0229-321-3214-32-87.

Input Specification:

Each input file contains one test case. Each case gives a positive integer N (≤104) followed by N number segments. Each segment contains a non-negative integer of no more than 8 digits. All the numbers in a line are separated by a space.

Output Specification:

For each test case, print the smallest number in one line. Notice that the first digit must not be zero.

Sample Input:

5 32 321 3214 0229 87

Sample Output:

22932132143287

1、大致题意

给一些字符串，求它们拼接起来构成最小数字的方式

2、基本思路

让我们一起来见证 cmp 函数的强大之处！！~不是按照字典序排列就可以的，必须保证两个字符串构成的数字是最小的才行，所以 cmp函数写成 return a + b < b + a; 的形式，保证它排列按照能够组成的最小数字的形式排列。

因为字符串可能前面有0，这些要移除掉（用s.erase(s.begin())就可以了嗯 string如此神奇）。输出拼接后的字符串即可。

注意：如果移出了0之后发现 s.length() == 0了，说明这个数是0，那么要特别地输出这个0，否则会什么都不输出

3、解题思路

3.1 `string` 知识点

我在解题前，复习了 string 库的相关知识点，此题主要是 string 的 erase() 函数，这个函数有2种用法：

删除单个元素
删除一个区间内的所有元素

时间复杂度均为O(N)

include

using namespace std;
int main()
{

// 删除单个元素
string ss = "12345";
cout << "ss: " << ss << " " << endl;
ss.erase(ss.begin()+4);
cout << "ss.erase(ss.begin()+24: " << ss << endl;
// 删除1个区间内所有元素
cout << endl;
ss = "678910";
cout << "ss: " << ss << " " << endl;
ss.erase(ss.begin()+2, ss.end()-1);
cout << "ss.erase(ss.begin()+2, ss.end()-1): " << ss << endl;
// 从起始位置，删除x个字符
cout << endl;
ss = "678910";
cout << "ss: " << ss << " " << endl;
ss.erase(3,3);
cout << "ss.erase(3,3): " << ss;
return 0;

}

输出：

ss: 12345
ss.erase(ss.begin()+24: 1234
ss: 678910
ss.erase(ss.begin()+2, ss.end()-1): 670
ss: 678910
ss.erase(3,3): 678
Process returned 0 (0x0)   execution time : 0.018 s
Press any key to continue.

3.2 AC代码

#include<vector>
#include<iostream>
#include<algorithm>
using namespace std;
int n;
vector<string> str;
bool cmp(string a, string b) {
    return a+b<b+a;
}
int main() {
    cin>>n;
    string s;
    for(int i=0; i<n; i++){
        cin>>s;
        str.push_back(s);
    }
    sort(str.begin(), str.end(), cmp);
    string ans;
    for(int i=0; i<n; i++)
        ans+=str[i];
    while(ans.size() != 0 && ans[0] == '0')
        ans.erase(ans.begin());
    if(ans.size() == 0) cout << 0;
    else cout << ans;
    return 0;
}