1+ /**
2+ * Brute force
3+ * @param {number[] } height
4+ * @return {number }
5+ */
6+ var trapBF = function ( height ) {
7+ let result = 0 ;
8+ for ( let i = 1 ; i < height . length - 1 ; i ++ ) {
9+ let leftMax = 0 , rightMax = 0 ;
10+ for ( let j = i ; j >= 0 ; j -- )
11+ leftMax = Math . max ( leftMax , height [ j ] ) ;
12+ 13+ for ( let j = i ; j < height . length ; j ++ )
14+ rightMax = Math . max ( rightMax , height [ j ] )
15+ 16+ result += Math . min ( leftMax , rightMax ) - height [ i ] ;
17+ }
18+ return result ;
19+ } ;
20+ 21+ /**
22+ * Dynamic Programming
23+ * @param {number[] } height
24+ * @return {number }
25+ */
26+ var trapDP = function ( height ) {
27+ let result = 0 ;
28+ let n = height . length ;
29+ let leftMax = [ ] , rightMax = [ ] ;
30+ 31+ leftMax [ 0 ] = height [ 0 ] ;
32+ rightMax [ n - 1 ] = height [ n - 1 ] ;
33+ 34+ for ( let i = 1 ; i < n - 1 ; i ++ ) {
35+ leftMax [ i ] = Math . max ( leftMax [ i - 1 ] , height [ i ] ) ;
36+ }
37+ 38+ for ( let i = n - 2 ; i >= 0 ; i -- ) {
39+ rightMax [ i ] = Math . max ( rightMax [ i + 1 ] , height [ i ] ) ;
40+ }
41+ 42+ for ( let i = 1 ; i < n - 1 ; i ++ ) {
43+ result += Math . min ( leftMax [ i ] , rightMax [ i ] ) - height [ i ] ;
44+ }
45+ return result ;
46+ }
47+ 48+ /**
49+ * Two Pointer
50+ * @param {number[] } height
51+ * @return {number }
52+ */
53+ var trap = function ( height ) {
54+ let left = 0 , right = height . length - 1 ;
55+ let leftMax = 0 , rightMax = 0 ;
56+ let result = 0 ;
57+ 58+ while ( left < right ) {
59+ if ( height [ left ] < height [ right ] ) {
60+ height [ left ] >= leftMax ? ( leftMax = height [ left ] ) : result += ( leftMax - height [ left ] ) ;
61+ left ++ ;
62+ } else {
63+ height [ right ] >= rightMax ? ( rightMax = height [ right ] ) : result += ( rightMax - height [ right ] ) ;
64+ right -- ;
65+ }
66+ }
67+ return result ;
68+ }
69+ 70+ console . log ( trap ( [ 0 , 1 , 0 , 2 , 1 , 0 , 1 , 3 , 2 , 1 , 2 , 1 ] ) )
71+ console . log ( trap ( [ 1 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 0 , 1 ] ) )
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