add new solutions

solutions/15/q1536/solution.go

@@ -0,0 +1,44 @@
+// Package q1536 implements a solution for https://leetcode.com/problems/minimum-swaps-to-arrange-a-binary-grid/
+package q1536
+
+func minSwaps(grid [][]int) int {
+	n := len(grid)
+
+	zeros := grid[0] // reuse memory
+	for i := range grid {
+		z := n - 1
+		for z >= 0 && grid[i][z] == 0 {
+			z--
+		}
+		zeros[i] = n - z - 1
+	}
+
+	steps := 0
+	for row := range n - 1 {
+		needZ := n - row - 1
+		if zeros[row] >= needZ {
+			continue
+		}
+
+		// Find a row with at lease needZ zeros at the end
+		found := -1
+		for i := row + 1; i < n; i++ {
+			if zeros[i] >= needZ {
+				found = i
+				break
+			}
+		}
+		if found == -1 {
+			return -1
+		}
+
+		steps += found - row
+		t := zeros[found]
+		copy(zeros[row+1:found+1], zeros[row:found])
+		zeros[row] = t
+	}
+
+	return steps
+}
+
+var _ = minSwaps

solutions/15/q1545/solution.go

@@ -0,0 +1,30 @@
+// Package q1545 implements a solution for https://leetcode.com/problems/find-kth-bit-in-nth-binary-string/
+package q1545
+
+var buf = make([]byte, 1<<20)
+var bufLen = 1
+
+func init() { buf[0] = '0' }
+
+func generate() {
+	buf[bufLen] = '1'
+	newTail := bufLen * 2
+	for i := range bufLen {
+		switch buf[i] {
+		case '0':
+			buf[newTail-i] = '1'
+		case '1':
+			buf[newTail-i] = '0'
+		}
+	}
+	bufLen = newTail + 1
+}
+
+func findKthBit(n, k int) byte {
+	for bufLen < k {
+		generate()
+	}
+	return buf[k-1]
+}
+
+var _ = findKthBit

solutions/15/q1582/solution.go

@@ -0,0 +1,39 @@
+// Package q1582 implements a solution for https://leetcode.com/problems/special-positions-in-a-binary-matrix/
+package q1582
+
+func numSpecial(mat [][]int) int {
+	hPos := make([]int, len(mat))
+	vPos := make([]int, len(mat[0]))
+	for i := range vPos {
+		vPos[i] = -1
+	}
+
+	for row := range mat {
+		hPos[row] = -1
+		for col, val := range mat[row] {
+			if val == 1 {
+				if hPos[row] >= 0 {
+					hPos[row] = -2
+				} else if hPos[row] == -1 {
+					hPos[row] = col
+				}
+
+				if vPos[col] >= 0 {
+					vPos[col] = -2
+				} else if vPos[col] == -1 {
+					vPos[col] = row
+				}
+			}
+		}
+	}
+
+	pairs := 0
+	for i := range hPos {
+		if hPos[i] >= 0 && vPos[hPos[i]] == i {
+			pairs++
+		}
+	}
+	return pairs
+}
+
+var _ = numSpecial