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@@ -0,0 +1,44 @@
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+package com.example.modifier;
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+
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+import org.junit.Test;
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+
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+import java.util.HashMap;
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+import java.util.concurrent.ConcurrentHashMap;
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+
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+public class Luhn {
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+ private static char[] CHECKS = "0987654321".toCharArray();
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+
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+ public static boolean isValidLuhn(String number) {
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+
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+ if (number == null) {
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+ return false;
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+ }
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+
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+ char[] chs = number.toCharArray();
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+ int count = 0;
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+
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+ for (int i = chs.length - 2, k = 1; i >= 0; i--, k++) {
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+
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+ // 不是数字字符时直接返回 false
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+ if (chs[i] < '0' || chs[i] > '9') {
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+ return false;
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+ }
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+
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+ // 偶位数字 * 2，奇位不乘
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+ int num = (chs[i] - '0') << (k & 1);
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+
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+ // 累加
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+ count += num % 10 + num / 10;
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+ }
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+
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+ System.out.println(CHECKS[count % 10]);
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+ // 对校验位进行比对
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+ return (chs[chs.length - 1] == CHECKS[count % 10]);
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+ }
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+
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+ @Test
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+ public void test() {
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+ assert isValidLuhn("89660166219355995276");
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+
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+ }
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+}
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