TrappedWater.java

JAVA/TrapWater.java

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+import java.util.*;
+
+public class ArrayCC{
+
+  public static int trappedWater(int height[]){
+    int n = height.length;
+    // calculate left max boundary - array
+    int[] leftMax = new int[n];
+    leftMax[0] = height[0];
+    for(int i=1; i<n; i++){
+      leftMax[i] = Math.max(height[i], leftMax[i-1]);
+    }
+
+    // calculate right max boundary - array
+     int[] rightMax = new int[n];
+    rightMax[n-1] = height[n-1];
+    for(int i=n-2; i>=0; i--){
+      rightMax[i] = Math.max(height[i], rightMax[i+1]);
+    }
+
+    int trappedWater = 0;
+    // loop
+    for(int i=0; i<n; i++){
+      // water level = min(leftmax bound, rightmax bound)
+      int waterLevel = Math.min(leftMax[i], rightMax[i]);
+
+      // trapped water = water level - height[i]
+      trappedWater += waterLevel - height[i];
+    }
+    return trappedWater;
+  }
+
+  public static void main(String[] args){
+     int[] height = {4,2,0,6,3,2,5};
+       System.out.println(trappedWater(height));
+   }
+}
+