'commit'

TangDou/AcWing/SegmentTree/P3919.cpp

@@ -0,0 +1,98 @@
+#include <algorithm>
+#include <cstdio>
+#include <cmath>
+#include <cstring>
+
+using namespace std;
+const int N = 1000010;
+
+struct Node {
+    int l, r, v;
+} tr[N << 5];
+int root[N], idx;
+int n, m, a[N];
+
+//快读
+int read() {
+    int x = 0, f = 1;
+    char ch = getchar();
+    while (ch < '0' || ch > '9') {
+        if (ch == '-') f = -1;
+        ch = getchar();
+    }
+    while (ch >= '0' && ch <= '9') {
+        x = (x << 3) + (x << 1) + (ch ^ 48);
+        ch = getchar();
+    }
+    return x * f;
+}
+
+// build的原因，是因为有初始值，版本0不是空的
+void build(int &u, int l, int r) {
+    u = ++idx;
+    if (l == r) {
+        tr[u].v = a[l];
+        return;
+    }
+    int mid = (l + r) >> 1;
+    build(tr[u].l, l, mid);
+    build(tr[u].r, mid + 1, r);
+}
+
+void update(int &u, int l, int r, int x, int v) {
+    tr[++idx] = tr[u];
+    u = idx;
+    if (l == r) {
+        tr[idx].v = v;
+        return;
+    }
+    int mid = (l + r) >> 1;
+    if (mid >= x)
+        update(tr[u].l, l, mid, x, v);
+    else
+        update(tr[u].r, mid + 1, r, x, v);
+}
+
+int query(int u, int l, int r, int x) {
+    if (l == r) return tr[u].v;
+    int mid = (l + r) >> 1;
+    if (mid >= x)
+        return query(tr[u].l, l, mid, x);
+    else
+        return query(tr[u].r, mid + 1, r, x);
+}
+/*
+答案：
+59
+87
+41
+87
+88
+46
+*/
+int main() {
+//文件输入输出
+#ifndef ONLINE_JUDGE
+    freopen("P3919.in", "r", stdin);
+#endif
+    n = read(), m = read();
+    for (int i = 1; i <= n; i++) a[i] = read();
+
+    //构建主席树,因为有初始化值a[i]
+    build(root[0], 1, n);
+
+    for (int i = 1; i <= m; i++) {
+        int x = read(), op = read(), y = read();
+        if (op == 1) {
+            // op=1:修改 x这个版本,管辖范围[1,n],将a[y]的值，即y这个位置,修改为v
+            int v = read();
+            root[i] = root[x];
+            update(root[i], 1, n, y, v);
+        } else {
+            // op=2：访问版本x中，y这个位置上的值
+            root[i] = root[x];
+            printf("%d\n", query(root[i], 1, n, y));
+        }
+    }
+    return 0;
+}