zoukankan      html  css  js  c++  java
  • Minimum number of steps CodeForces

    D. Minimum number of steps
    time limit per test
    1 second
    memory limit per test
    256 megabytes
    input
    standard input
    output
    standard output

    We have a string of letters 'a' and 'b'. We want to perform some operations on it. On each step we choose one of substrings "ab" in the string and replace it with the string "bba". If we have no "ab" as a substring, our job is done. Print the minimum number of steps we should perform to make our job done modulo 109 + 7.

    The string "ab" appears as a substring if there is a letter 'b' right after the letter 'a' somewhere in the string.

    Input

    The first line contains the initial string consisting of letters 'a' and 'b' only with length from 1 to 106.

    Output

    Print the minimum number of steps modulo 109 + 7.

    Examples
    input
    Copy
    ab
    output
    Copy
    1
    input
    Copy
    aab
    output
    Copy
    3
    Note

    The first example: "ab →  "bba".

    The second example: "aab →  "abba →  "bbaba →  "bbbbaa".

    从后向前 遍历

    每个a都会把它后边的b变到后边 且乘二  

    而每个a后边b的个数 即为当前a变化的次数

    #include <bits/stdc++.h>
    #define mem(a, b) memset(a, b, sizeof(a))
    using namespace std;
    typedef long long LL;
    const int maxn = 1000010, INF = 0x7fffffff;
    const int MOD = 1e9 + 7;
    int n;
    string str;
    
    
    int main()
    {
    
        cin >> str;
        int len = str.size();
        int ans = 0, cnt = 0;
        for(int i = len - 1; i >= 0; i--)
        {
            if(str[i] == 'b')
                cnt++;
            else
            {
                ans = (ans + cnt) % MOD;
                cnt = (cnt * 2) % MOD;
            }
    
        }
        cout << ans << endl;
    
    
    
    
        return 0;
    }
    D. Minimum number of steps
    time limit per test
    1 second
    memory limit per test
    256 megabytes
    input
    standard input
    output
    standard output

    We have a string of letters 'a' and 'b'. We want to perform some operations on it. On each step we choose one of substrings "ab" in the string and replace it with the string "bba". If we have no "ab" as a substring, our job is done. Print the minimum number of steps we should perform to make our job done modulo 109 + 7.

    The string "ab" appears as a substring if there is a letter 'b' right after the letter 'a' somewhere in the string.

    Input

    The first line contains the initial string consisting of letters 'a' and 'b' only with length from 1 to 106.

    Output

    Print the minimum number of steps modulo 109 + 7.

    Examples
    input
    Copy
    ab
    output
    Copy
    1
    input
    Copy
    aab
    output
    Copy
    3
    Note

    The first example: "ab →  "bba".

    The second example: "aab →  "abba →  "bbaba →  "bbbbaa".

    自己选择的路,跪着也要走完。朋友们,虽然这个世界日益浮躁起来,只要能够为了当时纯粹的梦想和感动坚持努力下去,不管其它人怎么样,我们也能够保持自己的本色走下去。
  • 相关阅读:
    数据库-插入数据insert,更新数据update,删除数据delete
    前端移动端监听键盘上的 开始/搜索 按键,并触发函数
    移动端input输入框把页面顶起, 收起键盘页面复原不了问题
    微信小程序如何把接口调用成功的回调函数返回的参数return出去?(promise就可以解决!!)
    js判断json数据是否存在某字段的方法
    微信小程序、微信公众号、H5之间能相互跳转
    java JDK的安装和环境配置(windows10)
    接私活必备的 10 个开源项目
    小程序获取自定义属性之e.target与e.currentTarget
    小程序中webview内嵌h5页面
  • 原文地址:https://www.cnblogs.com/WTSRUVF/p/10638833.html
Copyright © 2011-2022 走看看