Histogram - Visualization

Heights: $[2, 1, 5, 6, 2, 3]$. Maintain increasing stack of indices. $i=0$, h=$2$: push $0$. Stack: $[0]$

$i=1$, h=$1$: $1 < 2$, pop $0$. Area = $2 \times (1 - (-1) - 1) = 2$.

Push $1$. Stack: $[1]$

$i=2$, h=$5$: push $2$. Stack: $[1, 2]$

$i=3$, h=$6$: push $3$. Stack: $[1, 2, 3]$

$i=4$, h=$2$: pop $3$, area = $6 \times 1 = 6$.

Pop $2$, area = $5 \times 2 = 10$. Push $4$. Stack: $[1, 4]$

$i=5$, h=$3$: push $5$. Stack: $[1, 4, 5]$

Pop remaining: areas $3$, $8$, $6$. Maximum: $10$.