题解 | #字符串距离#

import java.util.Scanner;

public class Main {
    public static void main(String[] args){
        Scanner in = new Scanner(System.in);

        while(in.hasNext()){
            solution1(in);
        }
    }

    /**
     * 模拟法: 前缀和
     * 
     * pre[i]表示字符串S前i个字符中a的个数
     * 
     * @param in
     */
    private static void solution1(Scanner in){
        String S = in.nextLine();
        String T = in.nextLine();

        int sLen = S.length();
        int tLen = T.length();

        int[] pre = new int[sLen+1];
        for(int i=1; i<=sLen; i++){
            if(S.charAt(i-1) == 'a'){
                pre[i] = pre[i-1]+1;
            }else{
                pre[i] = pre[i-1];
            }
        }

        int gap = sLen-tLen+1;
        long result = 0;
        char tChar;
        int aCount;
        for(int i=0; i<tLen; i++){
            tChar = T.charAt(i);
            aCount = pre[i+gap]-pre[i];
            if(tChar == 'b'){
                result += aCount;
            }else{
                result += gap-aCount;
            }
        }

        System.out.println(result);
    }
}