面试题 35: 第一个只出现一次的字符

package ween_2;

import java.util.LinkedHashMap;

/**
* 剑指offer: 在字符串中找出第一个只出现一次的字符.
* 方法:1.比较,O(n^2);2.hash表(推荐)-linkedHashMap
* 测试用例:功能测试(存在只出现一次的字符;不存在;所有字符都只出现一次)
* 特殊输入测试(字符串为空)
* @author dingding
* Date:2017-6-19 9:00
* Declaration: All Rights Reserved!
*/
public class FindNumsAppearOnce {

public static void main(String[] args) {
test1();
test2();
test3();
test4();
}

private static Character findFirstNumAppearOnce (String string){
if (string==null) {
return null;
}
char[] sChar = string.toCharArray();
LinkedHashMap<Character, Integer> hashChar = new LinkedHashMap<Character,Integer>();
for (char item:sChar){
if (hashChar.containsKey(item)) {
hashChar.put(item, hashChar.get(item)+1);
}else {
hashChar.put(item,1);
}
}
//遍历
for (char key:hashChar.keySet()){
if (hashChar.get(key)==1) {
return key;
}
}
return null;
}
/*================测试用例======================*/
//存在只出现一次
private static void test1() {
System.out.println(findFirstNumAppearOnce("abaccdeff"));
System.out.println("=====================");
}
//不存在
private static void test2() {
System.out.println(findFirstNumAppearOnce("aaccddff"));
System.out.println("=====================");
}
//每个字符都只出现一次
private static void test3() {
System.out.println(findFirstNumAppearOnce("abcdefgh"));
System.out.println("=====================");
}
//字符串为空
private static void test4() {
System.out.println(findFirstNumAppearOnce(""));
}

}

参考文献