ADVANCED DATA STRUCTURES PROGRAM • LEVEL 21 — PLACEMENT-ORIENTED STRUCTURES

Apply Range Updates with Lazy Propagation

Learn how to apply range updates with lazy propagation using a clear C program.

AdvancedInterview patternRange and stream queries

PROBLEM UNDERSTANDING

Input and expected output

Sample input

No input required

Sample output

Point 2 = 7 Point 4 = 2

COMPLETE C PROGRAM

Complete C implementation

#include <stdio.h>

void push(int tree[],int lazy[],int node,int left,int right){if(lazy[node]){tree[node]+=(right-left+1)*lazy[node];if(left!=right){lazy[node*2]+=lazy[node];lazy[node*2+1]+=lazy[node];}lazy[node]=0;}}void update(int tree[],int lazy[],int node,int left,int right,int ql,int qr,int value){push(tree,lazy,node,left,right);if(qr<left||right<ql)return;if(ql<=left&&right<=qr){lazy[node]+=value;push(tree,lazy,node,left,right);return;}int middle=(left+right)/2;update(tree,lazy,node*2,left,middle,ql,qr,value);update(tree,lazy,node*2+1,middle+1,right,ql,qr,value);tree[node]=tree[node*2]+tree[node*2+1];}int query(int tree[],int lazy[],int node,int left,int right,int index){push(tree,lazy,node,left,right);if(left==right)return tree[node];int middle=(left+right)/2;return index<=middle?query(tree,lazy,node*2,left,middle,index):query(tree,lazy,node*2+1,middle+1,right,index);}

int main(void)
{
    int tree[40]={0},lazy[40]={0};update(tree,lazy,1,0,4,1,3,5);update(tree,lazy,1,0,4,2,4,2);printf("Point 2 = %d Point 4 = %d\n",query(tree,lazy,1,0,4,2),query(tree,lazy,1,0,4,4));return 0;
}

CURRENT STEP

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SELECTED LINE

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EXPECTED OUTPUT FOR THE SAMPLE

Point 2 = 7 Point 4 = 2

0%Step 0 of 0

PROGRAM EXPLANATION

Algorithm and explanation

Read the required input values.
Delay a fully covered range update at its node and push it only when descendants are needed.
Display the computed result.

Delay a fully covered range update at its node and push it only when descendants are needed.

EFFICIENCY

Time and space complexity

Time complexity

O(log n) update/query

Auxiliary space

O(n)

DEBUGGING CHECKLIST

Common mistakes

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Use the correct format specifier for every variable.

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Initialize variables before using their values.

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Check braces, semicolons and input order carefully.

Try it yourself

Practice: Run the program with the sample input, predict its output, and then test one boundary case of your own.