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add a solution for 3178

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src
- main/java/com/fishercoder/solutions/fourththousand
  - _3178.java
- test/java/com/fishercoder/fourththousand
  - _3178Test.java

+24

-0

lines changed

Lines changed: 21 additions & 0 deletions

Original file line number	Diff line number	Diff line change
`@@ -16,4 +16,25 @@ public int numberOfChild(int n, int k) {`
`16`	`16`	`}`
`17`	`17`	`}`
`18`	`18`	`}`
	`19`	`+`
	`20`	`+publicstaticclassSolution2 {`
	`21`	`+/**`
	`22`	`+ * Also, my completely original solution, much more elegant and efficient.`
	`23`	`+ */`
	`24`	`+publicintnumberOfChild(intn,intk) {`
	`25`	`+//n - 1 is the number of steps is takes to finish from one end to the other`
	`26`	`+// 2 * (n - 1) is the whole round trip, so after this, it's back to the starting point`
	`27`	`+//so we only need to handle the modulo remainder of 2 * (n - 1)`
	`28`	`+k =k % ((n -1) *2);`
	`29`	`+if (k <n) {`
	`30`	`+//in this case, we can directly return k`
	`31`	`+returnk;`
	`32`	`+ }else {`
	`33`	`+//in this case, it's in the reverse direction, we deduct the number of steps needed to finish the forward direction first`
	`34`	`+k -=n -1;`
	`35`	`+//then return the correct child index`
	`36`	`+returnn -k -1;`
	`37`	`+ }`
	`38`	`+ }`
	`39`	`+ }`
`19`	`40`	`}`

Lines changed: 3 additions & 0 deletions

Original file line number	Diff line number	Diff line change
`@@ -8,15 +8,18 @@`
`8`	`8`
`9`	`9`	`publicclass_3178Test {`
`10`	`10`	`privatestatic_3178.Solution1solution1;`
	`11`	`+privatestatic_3178.Solution2solution2;`
`11`	`12`
`12`	`13`	`@BeforeEach`
`13`	`14`	`publicvoidsetup() {`
`14`	`15`	`solution1 =new_3178.Solution1();`
	`16`	`+solution2 =new_3178.Solution2();`
`15`	`17`	`}`
`16`	`18`
`17`	`19`	`@Test`
`18`	`20`	`publicvoidtest1() {`
`19`	`21`	`assertEquals(1,solution1.numberOfChild(3,5));`
	`22`	`+assertEquals(1,solution2.numberOfChild(3,5));`
`20`	`23`	`}`
`21`	`24`
`22`	`25`	`@Test`

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