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Update TrappingRainWater.cpp #3

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77 changes: 25 additions & 52 deletions TrappingRainWater/TrappingRainWater.cpp
Original file line number Diff line number Diff line change
@@ -1,58 +1,31 @@
// O(n) time, O(n) space
class Solution {
public:
int trap(int A[], int n) {
// Start typing your C/C++ solution below
// DO NOT write int main() function

int max_from_left[n];
int max_from_right[n];

max_from_left[0] = A[0];
for (int i = 1; i < n; i++)
max_from_left[i] = max(max_from_left[i-1], A[i]);

max_from_right[n-1] = A[n-1];
for (int i = n - 2; i >= 0; i--)
max_from_right[i] = max(max_from_right[i+1], A[i]);

int water = 0;
for (int i = 1; i < n - 1; i++) {
int min_height = min(max_from_left[i-1], max_from_right[i+1]);
if (min_height > A[i])
water += min_height - A[i];
}
return water;
}
};
if(n<=1)
return 0;
int start = 0;
int end = n-1;

// O(n) time, O(1) space
class Solution {
public:
int trap(int A[], int n) {
int maxh = 0;
int water = 0;
int temp = 0;
for (int i = 0; i < n; i++) {
if (A[i] <= maxh) {
temp += maxh - A[i];
} else {
maxh = A[i];
water += temp;
temp = 0;
}
}
maxh = 0;
temp = 0;
for (int i = n - 1; i >= 0; i--) {
if (A[i] < maxh) {
temp += maxh - A[i];
} else {
maxh = A[i];
water += temp;
temp = 0;
}
}
return water;
int leftMax = A[start];
int rightMax = A[end];

int capacity;
while(start < end){
if(leftMax <= rightMax){
if(A[start+1] < leftMax){
capacity += (leftMax - A[start+1]);
}else{
leftMax = A[start+1];
}
start++;
}else{
if(A[end-1] < rightMax){
capacity += (rightMax - A[end-1]);
}else
rightMax = A[end-1];
end--;
}
}
return capacity;
}
};