Valid Password

Problem

In 1-9 keypad one key is not working. If someone enters a password then not working key will not be entered. You have given expected password and entered password. Check that entered password is valid or not. Ex: entered 164, expected 18684 (you need to take care as when u enter18684 and 164 only both will be taken as 164 input)

Solution

有几种情况需要考虑下， 

1. 没有按到过坏的键

2. 1864， 1684.  坏的是8， 坏的键又出现一次

2. expect有可能是186848888，要继续检查直到长度相等

public static boolean validPassword(String expect, String actual) {
    char faultKey = '\0'; //initial fault key
    int i=0, j=0;    //two pointer for each string
    for(; i<actual.length() && j<expect.length(); j++) {
        if(actual.charAt(i) != expect.charAt(j)) {
            if(faultKey == '\0')    faultKey = expect.charAt(j);    //record fault key
            else if(faultKey != expect.charAt(j))    return false;    //found second fault key
            i--;
        }
        i++;
    }
    
    for(int k=0; k<expect.length() ;k++) {
        if(faultKey == expect.charAt(k)) return false;            
    }
    //fault key may require press many times after that
    while(j<expect.length() && expect.charAt(j)==faultKey)    j++;
    
    return (i==actual.length() && j==expect.length() && faultKey == '\0') ? true : false;
}