add new solutions

solutions/2/q201/solution.go

@@ -0,0 +1,21 @@
+package q201
+
+func rangeBitwiseAnd(left int, right int) int {
+	ret := left & right
+	for i := ret + 1; i < right; {
+		ret &= i
+		if ret == 0 {
+			return 0
+		}
+
+		// Find first non-zero bit
+		t := 1
+		for i|t != i {
+			t <<= 1
+		}
+		i += t
+	}
+	return ret
+}
+
+var _ = rangeBitwiseAnd

solutions/2/q210/solution.go

@@ -0,0 +1,34 @@
+package q210
+
+func findOrder(numCourses int, prerequisites [][]int) []int {
+	ndeps := make([]int, numCourses)
+	revDeps := make([][]int, numCourses)
+	ret := make([]int, 0, numCourses)
+
+	for i := range prerequisites {
+		c, dep := prerequisites[i][0], prerequisites[i][1]
+		ndeps[c]++
+		revDeps[dep] = append(revDeps[dep], c)
+	}
+
+	for i := range ndeps {
+		if ndeps[i] == 0 {
+			ret = append(ret, i)
+		}
+	}
+	for i := 0; i < len(ret); i++ {
+		for _, c := range revDeps[ret[i]] {
+			ndeps[c]--
+			if ndeps[c] == 0 {
+				ret = append(ret, c)
+			}
+		}
+	}
+
+	if len(ret) != numCourses {
+		return nil
+	}
+	return ret
+}
+
+var _ = findOrder

solutions/2/q289/solution.go

@@ -0,0 +1,41 @@
+package q289
+
+func countLiveNeighbors(board [][]int, row, col int) int {
+	cnt := 0
+	for r := row - 1; r <= row+1; r++ {
+		for c := col - 1; c <= col+1; c++ {
+			if r == row && c == col || r < 0 || c < 0 || r >= len(board) || c >= len(board[0]) {
+				continue
+			}
+			cnt += board[r][c] & 1
+		}
+	}
+	return cnt
+}
+
+func gameOfLife(board [][]int) {
+	for r := range board {
+		for c := range board[r] {
+			neighbors := countLiveNeighbors(board, r, c)
+			if board[r][c]&1 == 1 {
+				switch {
+				case neighbors < 2 || neighbors > 3:
+					// die
+				default:
+					board[r][c] |= 2 // survive
+				}
+			} else if neighbors == 3 {
+				board[r][c] |= 2 // birth
+			}
+		}
+	}
+
+	// Next generation
+	for r := range board {
+		for c := range board[r] {
+			board[r][c] >>= 1
+		}
+	}
+}
+
+var _ = gameOfLife