Solution.go

func maximalRectangle(matrix []string) int {
	if len(matrix) == 0 {
		return 0
	}
	n := len(matrix[0])
	heights := make([]int, n)
	ans := 0
	for _, row := range matrix {
		for j, v := range row {
			if v == '1' {
				heights[j]++
			} else {
				heights[j] = 0
			}
		}
		ans = max(ans, largestRectangleArea(heights))
	}
	return ans
}

func largestRectangleArea(heights []int) int {
	res, n := 0, len(heights)
	var stk []int
	left, right := make([]int, n), make([]int, n)
	for i := range right {
		right[i] = n
	}
	for i, h := range heights {
		for len(stk) > 0 && heights[stk[len(stk)-1]] >= h {
			right[stk[len(stk)-1]] = i
			stk = stk[:len(stk)-1]
		}
		if len(stk) > 0 {
			left[i] = stk[len(stk)-1]
		} else {
			left[i] = -1
		}
		stk = append(stk, i)
	}
	for i, h := range heights {
		res = max(res, h*(right[i]-left[i]-1))
	}
	return res
}

func max(a, b int) int {
	if a > b {
		return a
	}
	return b
}