update solution 0031 & 0048

website/content/ChapterFour/0001~0099/0031.Next-Permutation.md

@@ -57,6 +57,7 @@ Output: [1]
 ```go
 package leetcode
 
+// 解法一
 func nextPermutation(nums []int) {
 	i, j := 0, 0
 	for i = len(nums) - 2; i >= 0; i-- {
@@ -86,6 +87,47 @@ func reverse(nums *[]int, i, j int) {
 func swap(nums *[]int, i, j int) {
 	(*nums)[i], (*nums)[j] = (*nums)[j], (*nums)[i]
 }
+
+// 解法二
+// [2,(3),6,5,4,1] -> 2,(4),6,5,(3),1 -> 2,4, 1,3,5,6
+func nextPermutation1(nums []int) {
+	var n = len(nums)
+	var pIdx = checkPermutationPossibility(nums)
+	if pIdx == -1 {
+		reverse(&nums, 0, n-1)
+		return
+	}
+
+	var rp = len(nums) - 1
+	// start from right most to leftward,find the first number which is larger than PIVOT
+	for rp > 0 {
+		if nums[rp] > nums[pIdx] {
+			swap(&nums, pIdx, rp)
+			break
+		} else {
+			rp--
+		}
+	}
+	// Finally, Reverse all elements which are right from pivot
+	reverse(&nums, pIdx+1, n-1)
+}
+
+// checkPermutationPossibility returns 1st occurrence Index where
+// value is in decreasing order(from right to left)
+// returns -1 if not found(it's already in its last permutation)
+func checkPermutationPossibility(nums []int) (idx int) {
+	// search right to left for 1st number(from right) that is not in increasing order
+	var rp = len(nums) - 1
+	for rp > 0 {
+		if nums[rp-1] < nums[rp] {
+			idx = rp - 1
+			return idx
+		}
+		rp--
+	}
+	return -1
+}
+
 ```
 
 

website/content/ChapterFour/0001~0099/0048.Rotate-Image.md

@@ -99,6 +99,7 @@ You have to rotate the image **[in-place](https://en.wikipedia.org/wiki/In-plac
 ```go
 package leetcode
 
+// 解法一
 func rotate(matrix [][]int) {
 	length := len(matrix)
 	// rotate by diagonal 对角线变换
@@ -114,6 +115,50 @@ func rotate(matrix [][]int) {
 		}
 	}
 }
+
+// 解法二
+func rotate1(matrix [][]int) {
+	n := len(matrix)
+	if n == 1 {
+		return
+	}
+	/* rotate clock-wise = 1. transpose matrix => 2. reverse(matrix[i])
+
+	1   2  3  4      1   5  9  13        13  9  5  1
+	5   6  7  8  =>  2   6  10 14  =>    14  10 6  2
+	9  10 11 12      3   7  11 15        15  11 7  3
+	13 14 15 16      4   8  12 16        16  12 8  4
+
+	*/
+
+	for i := 0; i < n; i++ {
+		// transpose, i=rows, j=columns
+		// j = i+1, coz diagonal elements didn't change in a square matrix
+		for j := i + 1; j < n; j++ {
+			swap(matrix, i, j)
+		}
+		// reverse each row of the image
+		matrix[i] = reverse(matrix[i])
+	}
+}
+
+// swap changes original slice's i,j position
+func swap(nums [][]int, i, j int) {
+	nums[i][j], nums[j][i] = nums[j][i], nums[i][j]
+}
+
+// reverses a row of image, matrix[i]
+func reverse(nums []int) []int {
+	var lp, rp = 0, len(nums) - 1
+
+	for lp < rp {
+		nums[lp], nums[rp] = nums[rp], nums[lp]
+		lp++
+		rp--
+	}
+	return nums
+}
+
 ```