撬動offer：尋找丟失的數字
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0x01：算法題目
Missing Digit
Have the function MissingDigit(str) take the str parameter, which will be a simple mathematical formula with three numbers, a single operator (+, -, *, or /) and an equal sign (=) and return the digit that completes the equation. In one of the numbers in the equation, there will be an x character, and your program should determine what digit is missing. For example, if str is "3x + 12 = 46" then your program should output 4. The x character can appear in any of the three numbers and all three numbers will be greater than or equal to 0 and less than or equal to 1000000.
Examples
Input: "4 - 2 = x"
Output: 2
Input: "1x0 * 12 = 1200"
Output: 0
大概的意思：存在一個四則運算等式，包含三個數字、一個符號（可以是+、-、*、/）和一個等號（=）。其中三字數字是可以是等式成立的，在三個數字中有個數字中有一個數字的某一位是未知的，求這位的數字。
0x02：題解
import?java.util.HashMap;
import?java.util.Map;
import?java.util.Scanner;
public?class?MainCmd?{
????public?static?String?MissingDigit(String?str)?{
????????if?(str?==?null?||?str.trim().equals(""))?{
????????????return?str;
????????}
????????if?(!str.contains("="))?{
????????????return?str;
????????}
????????String[]?splitStr?=?str.split("=");
????????String?firstElement?=?splitStr[0];
????????if?(firstElement.contains("-")?||?firstElement.contains("+")?||?firstElement.contains("*")
????????????????||?firstElement.contains("/"))?{
????????????String[]?ele?=?firstElement.split("[\\+\\-\\*\\/]");
????????????String?eleOne?=?ele[0];
????????????String?eleTow?=?ele[1];
????????????String?eleThree?=?splitStr[1];
????????????String?result?=?"";
????????????if?(str.contains("+"))?{
????????????????result?=?process(eleOne,?eleTow,?eleThree,?"+");
????????????}?else?if?(str.contains("-"))?{
????????????????result?=?process(eleOne,?eleTow,?eleThree,?"-");
????????????}?else?if?(str.contains("*"))?{
????????????????result?=?process(eleOne,?eleTow,?eleThree,?"*");
????????????}?else?{
????????????????result?=?process(eleOne,?eleTow,?eleThree,?"/");
????????????}
????????????return?result;
????????}?else?{
????????????return?str;
????????}
????}
????public?static?boolean?checkContainX(String?str)?{
????????if?(str.contains("x"))?{
????????????return?true;
????????}
????????return?false;
????}
????private?static?String?process(String?eleOne,?String?eleTow,?String?eleThree,?String?syboml)?{
????????boolean?eleOneFlag?=?checkContainX(eleOne);
????????boolean?eleTowFlag?=?checkContainX(eleTow);
????????boolean?eleThreeFlag?=?checkContainX(eleThree);
????????long?result?=?0;
????????switch?(syboml)?{
????????case?"+":
????????????if(eleOneFlag){
????????????????result?=?Long.parseLong(eleThree)?-?Long.parseLong(eleTow);
????????????}else?if(eleTowFlag){
????????????????result?=?Long.parseLong(eleThree)?-?Long.parseLong(eleOne);
????????????}else?if(eleThreeFlag){
????????????????result?=?Long.parseLong(eleOne)?+?Long.parseLong(eleTow);
????????????}
????????????break;
????????case?"-":
????????????if(eleOneFlag){
????????????????result?=?Long.parseLong(eleThree)?+?Long.parseLong(eleTow);
????????????}else?if(eleTowFlag){
????????????????result?=?Long.parseLong(eleOne)?-?Long.parseLong(eleThree);
????????????}else?if(eleThreeFlag){
????????????????result?=?Long.parseLong(eleOne)?-?Long.parseLong(eleTow);
????????????}
????????????break;
????????case?"*":
????????????if(eleOneFlag){
????????????????result?=?Long.parseLong(eleThree)?/?Long.parseLong(eleTow);
????????????}else?if(eleTowFlag){
????????????????result?=?Long.parseLong(eleThree)?/?Long.parseLong(eleOne);
????????????}else?if(eleThreeFlag){
????????????????result?=?Long.parseLong(eleOne)?*?Long.parseLong(eleTow);
????????????}
????????????break;
????????case?"/":
????????????if(eleOneFlag){
????????????????result?=?Long.parseLong(eleThree)?*?Long.parseLong(eleTow);
????????????}else?if(eleTowFlag){
????????????????result?=?Long.parseLong(eleOne)?/?Long.parseLong(eleThree);
????????????}else?if(eleThreeFlag){
????????????????result?=?Long.parseLong(eleOne)?/?Long.parseLong(eleTow);
????????????}
????????????break;
????????}
????????String?retResult?=?"";
????????if(eleOneFlag){
????????????retResult?=?getX(result,?eleOne);
????????}else?if(eleTowFlag){
????????????retResult?=?getX(result,?eleTow);
????????}else?if(eleThreeFlag){
????????????retResult?=?getX(result,?eleThree);
????????}
????????return?retResult;
????}
????private?static?String?getX(Long?result,?String?ele)?{
????????String?target?=?String.valueOf(result);
????????char[]?targetChar?=?target.toCharArray();
????????char[]?eleChar?=?ele.toCharArray();
????????Map?mapper?=?new?HashMap();
????????for(int?i=0;?i????????????mapper.put(eleChar[i],?targetChar[i]);
????????}
????????return?String.valueOf(mapper.get('x'));
????}
????public?static?void?main(String[]?args)?{
????????Scanner?s?=?new?Scanner(System.in);
????????while(true){
????????????String?line?=?s.nextLine();
????????????line?=?line.replaceAll("?",?"");
????????????System.out.print(MissingDigit(line));
????????}
????}
} 這個是暴力破解出來的，集思廣益，看看大家有沒有比較優(yōu)的方案。
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