Lower Bound

Lower bound: First position where target could insert while keeping sorted. Index of first $\geq$ target.

Examples in $[1,3,5,5,7,9]$:

• Lower bound of $5$: index $2$
• Lower bound of $6$: index $4$
• Lower bound of $10$: index $6$ (past end)

Uses: First occurrence, count elements $<$ value, insert position.

More versatile than exact match. Check if lower bound equals target for exact match.