Solution as on 05-08-2022 10:00 pm

Author: knockcat

0307. Range Sum Query - Mutable.cpp

@@ -0,0 +1,127 @@
+class NumArray
+{
+public:
+    int arr[100005], seg[100005 * 4]; // for segment Tree
+    vector<int> ans;
+
+    void build(int ind, int low, int high)
+    {
+        if (high == low)
+        {
+            seg[ind] = arr[low];
+            return;
+        }
+        int mid = (low + high) / 2;
+        build(2 * ind + 1, low, mid);
+        build(2 * ind + 2, mid + 1, high);
+
+        // find max in range
+        // seg[ind] = max(seg[2 * ind + 1],seg[2 * ind + 2]);
+
+        // find sum in range
+        seg[ind] = seg[2 * ind + 1] + seg[2 * ind + 2];
+    }
+
+    int query(int ind, int low, int high, int l, int r)
+    {
+        if (low >= l && high <= r) // [ 1 - 1 ]
+            return seg[ind];
+
+        if (high < l || low > r)
+            // return INT_MIN; ( when we doing for max)
+            return 0;
+
+        int mid = (low + high) / 2;
+        int left = query(2 * ind + 1, low, mid, l, r);
+        int right = query(2 * ind + 2, mid + 1, high, l, r);
+        // return max(left, right);
+        return left + right;
+    }
+
+    void updateSeg(int idx, int low, int high, int index, int val)
+    {
+        // no overlap
+        if (index < low || index > high)
+            return;
+
+        // total overlap
+        if (low == high)
+        {
+            if (low == index)
+                seg[idx] = val;
+            return;
+        }
+
+        // partial overlap
+        int mid = (low + high) / 2;
+        updateSeg(2 * idx + 1, low, mid, index, val);      // low child
+        updateSeg(2 * idx + 2, mid + 1, high, index, val); // high child
+        seg[idx] = seg[2 * idx + 1] + seg[2 * idx + 2];
+    }
+
+    NumArray(vector<int> &nums)
+    {
+        ans = nums;
+        for (int i = 0; i < nums.size(); ++i)
+            arr[i] = nums[i];
+        build(0, 0, nums.size() - 1);
+    }
+
+    void update(int index, int val)
+    {
+        updateSeg(0, 0, ans.size() - 1, index, val);
+    }
+
+    int sumRange(int left, int right)
+    {
+        return query(0, 0, ans.size() - 1, left, right);
+    }
+};
+
+/**
+ * Your NumArray object will be instantiated and called as such:
+ * NumArray* obj = new NumArray(nums);
+ * obj->update(index,val);
+ * int param_2 = obj->sumRange(left,right);
+ */
+
+//  Another Approach
+
+class NumArray
+{
+public:
+    vector<int> ans;
+    int sum = 0;
+    NumArray(vector<int> &nums)
+    {
+        sum = 0;
+        ans = nums;
+        for (int i = 0; i < nums.size(); ++i)
+        {
+            sum += nums[i];
+        }
+    }
+
+    void update(int index, int val)
+    {
+        sum -= ans[index];
+        ans[index] = val;
+        sum += val;
+    }
+
+    int sumRange(int left, int right)
+    {
+        int res = sum;
+
+        for (int i = 0; i < left; ++i)
+        {
+            res -= ans[i];
+        }
+        for (int i = right + 1; i < ans.size(); ++i)
+        {
+            res -= ans[i];
+        }
+
+        return res;
+    }
+};