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TrappingRainWater.java
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TrappingRainWater.java
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package Leetcode;
/**
* @author kalpak
*
* Given n non-negative integers representing an elevation map where the width of each bar is 1, compute how much water it can trap after raining.
*
* Example 1:
* Input: height = [0,1,0,2,1,0,1,3,2,1,2,1]
* Output: 6
* Explanation: The above elevation map (black section) is represented by array [0,1,0,2,1,0,1,3,2,1,2,1]. In this case, 6 units of rain water (blue section) are being trapped.
*
* Example 2:
* Input: height = [4,2,0,3,2,5]
* Output: 9
*
* Constraints:
*
* n == height.length
* 0 <= n <= 3 * 104
* 0 <= height[i] <= 105
*/
public class TrappingRainWater {
public static int trap(int[] height) {
if(height == null || height.length == 0)
return 0;
int[] maxLeft = new int[height.length];
int[] maxRight = new int[height.length];
int[] waterContent = new int[height.length];
int result = 0;
// Initialize the maxLeft with the 1st element and maxRight with the last element.
maxLeft[0] = height[0];
maxRight[maxRight.length - 1] = height[height.length - 1];
for(int i = 1; i < height.length; i++) {
maxLeft[i] = Math.max(maxLeft[i - 1], height[i]);
}
for(int i = height.length - 2; i >= 0; i--)
maxRight[i] = Math.max(maxRight[i + 1], height[i]);
for(int i = 0; i < height.length; i++) {
waterContent[i] = Math.min(maxLeft[i], maxRight[i]) - height[i];
}
for(int water : waterContent)
result += water;
return result;
}
public static void main(String[] args) {
int[] arr = new int[]{0,1,0,2,1,0,1,3,2,1,2,1};
System.out.println(trap(arr));
}
}