Swift 每週五題 LeetCode(9)

嗨嗨～各位～最近深深有感體力追不上年紀ＱＱ即使每週運動2–3天,在經過兩天假日10小時的課程,還是得在週一休假放過自己><

正題開始～～

69. Sqrt(x) (Easy)

這是一題開根號的題目～
因為只需要return 整數所以我用了最～～簡單的方法ＸＤ

Sqrt(x) - LeetCode

func mySqrt(_ x: Int) -> Int {
    //    return Int(sqrt(Double(x))) 也可以直接call function
    var result = 0
    var i = 1
    while i*i <= x {
        result = i
        i += 1
    }
    return result
}

70. Climbing Stairs (Easy)

每一次可以走一步或是兩步,計算最後有幾種方式可以到達終點
https://leetcode.com/problems/climbing-stairs/

func climbStairs(_ n: Int) -> Int {
    var step = [0, 1 , 1]
    for i in 1...n + 1 {
        if i <= 2 {
            continue
        }
        step.append(step[i - 1] + step[i - 2])
    }
    return step.last!
}

73. Set Matrix Zeroes (Medium)

這裡需要把”原本”數字是0的位置的上下左右都改成0

Example :

Input: matrix = [[0,1,2,0],[3,4,5,2],[1,3,1,5]]
Output: [[0,0,0,0],[0,4,5,0],[0,3,1,0]]

原本是0的位置只有[0, 0] [3, 0]的位置,所以從此位置望上,下,左,右的位置的數字都改成0,[0,1,2,0] →[0,0,0,0]

func setZeroes(_ matrix: inout [[Int]]) {
    let m = matrix.count 
    let n = matrix[0].count
    var rows = [Int]() 
    var cols = [Int]()
    
    for i in 0..<m {
        for k in 0..<n{
            if matrix[i][k] == 0 {
                rows.append(i)
                cols.append(k)
            }
        }
    }
    
    for col in cols {
        for i in 0..<m {
            matrix[i][col] = 0
        }
    }
    for row in rows {
        for k in 0..<n {
            matrix[row][k] = 0
        }
    }
}

75. Sort Colors (Medium)

這題最大的重點就是不能直接用sort function,直接上解答

Sort Colors - LeetCode

func sortColors(_ nums: inout [Int]) {
    var min = 0
    var max = nums.count - 1
    var i = 0
    
    while i <= max {
        if nums[i] == 0 {
            nums.swapAt(i, min)
            min += 1
            i += 1
        } else if nums[i] == 1 {
            i += 1
        } else if i <= max && nums[i] == 2 {
            nums.swapAt(i, max)
            max -= 1
        }
    }
}
var color = [0, 1, 0]

76. Minimum Window Substring (Hard)

這題真的好難ＱＱ直接看答案然後想辦法裡解

Minimum Window Substring - LeetCode

func minWindow(_ s: String, _ t: String) -> String {
    
    guard s.count >= t.count else {
        return ""
    }
    
    let sStr = Array(s)
    let tStr = Array(t)
    
    var tCurr = [Character:Int]()
    for i in 0..<tStr.count {
        let letter = tStr[i]
        tCurr[letter, default: 0] += 1
    }
    
    var charsInWindow = 0
    var minStr = ""
    var minLen = Int.max
    var start = 0
    for end in 0..<sStr.count {
        let letter = sStr[end]
        if tCurr[letter] != nil {
            if tCurr[letter]! > 0 {
                charsInWindow += 1
            }
            tCurr[letter]! -= 1
        }
        while start<sStr.count &&
                (tCurr[sStr[start]] == nil ||
                 (tCurr[sStr[start]] != nil && tCurr[sStr[start]]! < 0)) {
            if tCurr[sStr[start]] != nil {
                tCurr[sStr[start]]! += 1
            }
            start += 1
        }
       
        if charsInWindow == tStr.count {
            if end-start+1 < minLen {
                minLen = end-start+1
                minStr = String(sStr[start...end])
            }
        }
    }
    return minStr
}