Fix "build" function in segment_tree.md

akoutian · web-flow · commit 77762abbac3a · 2023-12-20T20:45:55.000Z
Ensure that each node stores the maximum of its children. Otherwise the results of any query will be wrong, unless this node has been visited by an "update" query previously.
diff --git a/src/data_structures/segment_tree.md b/src/data_structures/segment_tree.md
@@ -694,7 +694,7 @@ void build(int a[], int v, int tl, int tr) {
         int tm = (tl + tr) / 2;
         build(a, v*2, tl, tm);
         build(a, v*2+1, tm+1, tr);
-        t[v] = 0;
+        t[v] = max(t[v*2], t[v*2 + 1]);
     }
 }
 

Original file line number	Diff line number	Diff line change
`@@ -694,7 +694,7 @@ void build(int a[], int v, int tl, int tr) {`
`694`	`694`	`int tm = (tl + tr) / 2;`
`695`	`695`	`build(a, v*2, tl, tm);`
`696`	`696`	`build(a, v*2+1, tm+1, tr);`
`697`		`- t[v] = 0;`
	`697`	`+ t[v] = max(t[v2], t[v2 + 1]);`
`698`	`698`	`}`
`699`	`699`	`}`
`700`	`700`