g0001_0100.s0042_trapping_rain_water.solution.go Maven / Gradle / Ivy

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104 LeetCode algorithm problem solutions

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package s0042_trapping_rain_water

// #Hard #Top_100_Liked_Questions #Top_Interview_Questions #Array #Dynamic_Programming #Two_Pointers
// #Stack #Monotonic_Stack #Dynamic_Programming_I_Day_9 #Udemy_Two_Pointers
// #Big_O_Time_O(n)_Space_O(1) #2024_03_12_Time_3_ms_(99.42%)_Space_5.4_MB_(97.01%)

func trap(height []int) int {
	if height == nil {
		return 0
	}
	l, r := 0, len(height)-1
	max_left, max_right := height[l], height[r]
	res := 0
	for l < r {
		if max_left < max_right {
			l++
			max_left = max(max_left, height[l])
			res += max_left - height[l]
		} else {
			r--
			max_right = max(max_right, height[r])
			res += max_right - height[r]
		}
	}
	return res
}

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