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`‎279. Perfect Squares.md‎`

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	`1`	`+# 100. Perfect Squares`
	`2`	`+`
	`3`	`+### 2020年07月30日`
	`4`	`+`
	`5`	+Given a positive integer n, find the least number of perfect square numbers (for example, `1, 4, 9, 16, ...`) which sum to n.
	`6`	`+`
	`7`	`+Example 1:`
	`8`	+```
	`9`	`+Input: n = 12`
	`10`	`+Output: 3`
	`11`	`+Explanation: 12 = 4 + 4 + 4.`
	`12`	+```
	`13`	`+`
	`14`	`+Example 2:`
	`15`	+```
	`16`	`+Input: n = 13`
	`17`	`+Output: 2`
	`18`	`+Explanation: 13 = 4 + 9.`
	`19`	+```
	`20`	`+`
	`21`	`+# Solution`
	`22`	`+`
	`23`	+```swift
	`24`	`+class Solution {`
	`25`	`+`
	`26`	`+ var cache = [Int: Int]()`
	`27`	`+ var perfectSquare = [Int]()`
	`28`	`+`
	`29`	`+ func findSum(count: Int, num: Int) -> Bool {`
	`30`	`+ switch count {`
	`31`	`+ case 0:`
	`32`	`+ return false`
	`33`	`+ case 1:`
	`34`	`+ guard let c = cache[num] else {`
	`35`	`+ return false`
	`36`	`+ }`
	`37`	`+ return c == 1`
	`38`	`+ default:`
	`39`	`+ if cache[num] != nil {`
	`40`	`+ return true`
	`41`	`+ }`
	`42`	`+ for sn in perfectSquare {`
	`43`	`+ if findSum(count: count - 1, num: num - sn) {`
	`44`	`+ cache[num] = count`
	`45`	`+ return true`
	`46`	`+ }`
	`47`	`+ }`
	`48`	`+ return false`
	`49`	`+ }`
	`50`	`+ }`
	`51`	`+`
	`52`	`+ func isPerfectSquare(n: Int) -> Bool {`
	`53`	`+ let sqN = Int(sqrt(Double(n)))`
	`54`	`+ return sqN * sqN == n`
	`55`	`+ }`
	`56`	`+`
	`57`	`+ func numSquares(_ n: Int) -> Int {`
	`58`	`+ guard n > 0 else {`
	`59`	`+ return 0`
	`60`	`+ }`
	`61`	`+ for i in 1...n {`
	`62`	`+ if isPerfectSquare(n: i) {`
	`63`	`+ perfectSquare.append(i)`
	`64`	`+ cache[i] = 1`
	`65`	`+ }`
	`66`	`+ }`
	`67`	`+ for i in 1...n {`
	`68`	`+ if findSum(count: i, num: n) {`
	`69`	`+ return i`
	`70`	`+ }`
	`71`	`+ }`
	`72`	`+ return n`
	`73`	`+ }`
	`74`	`+}`
	`75`	+```

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