Fix boundary condition in segment tree walk

lrvideckis · web-flow · commit 3beb2d193a58 · 2026-02-07T02:34:21.000-07:00
diff --git a/library/data_structures_[l,r]/seg_tree_uncommon/walk.hpp b/library/data_structures_[l,r]/seg_tree_uncommon/walk.hpp
@@ -15,7 +15,7 @@ int walk(int l, int r, const auto& f) {
   */
   while (l <= r) {
     int u = l + n, x = __lg(min(u & -u, r - l + 1));
-    if (f(s[u >> x])) r = l + (1 << x) - 1;
+    if (f(s[u >> x])) r = l + (1 << x) - 2;
     else l += 1 << x;
   }
   return -1;

Original file line number	Diff line number	Diff line change
`@@ -15,7 +15,7 @@ int walk(int l, int r, const auto& f) {`
`15`	`15`	`*/`
`16`	`16`	`while (l <= r) {`
`17`	`17`	`int u = l + n, x = __lg(min(u & -u, r - l + 1));`
`18`		`- if (f(s[u >> x])) r = l + (1 << x) - 1;`
	`18`	`+ if (f(s[u >> x])) r = l + (1 << x) - 2;`
`19`	`19`	`else l += 1 << x;`
`20`	`20`	`}`
`21`	`21`	`return -1;`