• Replace To Make Regular Bracket Sequence


    Replace To Make Regular Bracket Sequence

    You are given string s consists of opening and closing brackets of four kinds <>, {}, [], (). There are two types of brackets: opening and closing. You can replace any bracket by another of the same type. For example, you can replace < by the bracket {, but you can't replace it by ) or >.

    The following definition of a regular bracket sequence is well-known, so you can be familiar with it.

    Let's define a regular bracket sequence (RBS). Empty string is RBS. Let s1 and s2 be a RBS then the strings <s1>s2{s1}s2[s1]s2(s1)s2 are also RBS.

    For example the string "[[(){}]<>]" is RBS, but the strings "[)()" and "][()()" are not.

    Determine the least number of replaces to make the string s RBS.

    Input

    The only line contains a non empty string s, consisting of only opening and closing brackets of four kinds. The length of s does not exceed 106.

    Output

    If it's impossible to get RBS from s print Impossible.

    Otherwise print the least number of replaces needed to get RBS from s.

    Examples

    Input
    [<}){}
    Output
    2
    Input
    {()}[]
    Output
    0
    Input
    ]]
    Output
    Impossible

    题意:输入一行括号序列,左边括号可以和右括号抵消。右括号可以转换为其他类型右括号进行成对抵消。输出需要转换的个数。如果无法抵消输出"Impossible"
     1 #include <iostream>
     2 #include <stack>
     3 using namespace std;
     4 
     5 int main(){
     6     string input;
     7     while(cin >> input){
     8         int count = 0;
     9         stack<char> s;
    10         s.push(input[0]); //[ 
    11         for(int i = 1;i < input.length();i++){//<}){}
    12             if(s.size() > 0 && (s.top() == '[' || s.top() == '<' || s.top() == '(' || s.top() == '{')){
    13                 if(input[i] == ']' || input[i] == '>' || input[i] == ')' || input[i] == '}'){
    14                     if(!((s.top() == '[' && input[i] == ']') || 
    15                         (s.top() == '<' && input[i] == '>') || 
    16                         (s.top() == '(' && input[i] == ')') ||
    17                         (s.top() == '{' && input[i] == '}'))){
    18                         count++;
    19                     }
    20                     s.pop();
    21                 }else{
    22                     s.push(input[i]);
    23                 }
    24             }else{
    25                 s.push(input[i]);
    26             }
    27         }
    28         if(s.size() != 0){
    29             cout << "Impossible" << endl;
    30         }else{
    31             cout << count << endl;
    32         }
    33     }
    34 }



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  • 原文地址:https://www.cnblogs.com/jxust-jiege666/p/10778764.html
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