js-concepts: couting, range queries with two dimensional array

Author: baochau.dinh

Counting/index.js

@@ -0,0 +1,99 @@
+/**
+ * Problem 1: Given an array A has n elements.
+ * A (L, r, k) query is a query counts # elements equal to k from L to r
+ */
+
+function main(A) {
+  if (A.length === 0) return;
+
+  function solution(L, R, K) {
+    let count = 0;
+    for (let i = L; i <= R; i++) {
+      if (A[i] === K) count++;
+    }
+
+    return count;
+  }
+
+  return solution(3, 9, 3); // test
+}
+
+/**
+ * Problem 2: Given an array A has n elements.
+ * There are #Q queries (L_i, R_i, k) 1 <= i <= Q
+ */
+
+function main2(A) {
+  if (A.length === 0) return;
+
+  function solution(Q = [], K) {
+    let count = new Array(A.length).fill(0); // mảng cộng dồn, count[i] minh họa số phần tử bằng K trong đoạn từ 0 đến i
+    if (A[0] === K) count[0] = 1;
+    else count[0] = 0;
+    for (let i = 1; i < A.length; i++) {
+      if (A[i] === K) count[i] = count[i - 1] + 1;
+      else count[i] = count[i - 1];
+    }
+
+    for (let i = 0; i < Q.length; i++) {
+      let L = Q[i][0], R = Q[i][1];
+      console.log(count[R] - count[L]);
+    }
+
+    return;
+  }
+
+  return solution([[0, 3], [1, 2], [3, 9]], 2);
+}
+
+/**
+ * Given an array A has n elements
+ * There are #Q queries like (L_i, R_i, K_i) 1<= i <= Q
+ * Count 
+ */
+
+function main3(A) {
+  if (A.length === 0) return;
+
+  function solution(Q = []) {
+    let count = new Array(A.length).fill(0).map(x => new Array(100)); // count[i][K] đếm số lần xuất hiện của K trong đoạn từ 0 đến i
+    for (let i = 0; i < A.length; i++) {
+      for (let j = 0; j <= 2; j++) {
+        if (A[i] === j) {
+          count[i][j] = (i >= 1) ? count[i - 1][j] + 1 : 1
+        } else {
+          count[i][j] = (i >= 1) ? count[i - 1][j] : 0
+        }
+      }
+    }
+
+    for (let i = 0; i < Q.length; i++) {
+      let L = Q[i][0], R = Q[i][1], K = Q[i][2];
+      console.log(count[R][K] -  (L >= 1 ? count[L - 1][K] : 0));
+    }
+
+    return;
+  }
+
+  return solution([[0, 2, 2], [1, 2, 1], [0, 2, 1]]);
+}
+
+console.log(main3([1, 1, 1]));
+
+// function rangeQueries (A = []) {
+//   if (A.length === 0) return;
+//   let count = new Array(3).fill(0).map(x => new Array(3));
+
+//   for (let i = 0; i < A.length; i++) {
+//     for (let j = 0; j < 3; j++) {
+//       if (j === A[i]) {
+//         count[i][j] = (i >= 1) ? count[i - 1][j] + 1 : 1;
+//       } else {
+//         count[i][j] = (i >= 1) ? count[i - 1][j] : 0;
+//       }
+//     }
+//   }
+//   return;
+// }
+
+// console.log(rangeQueries([2, 1, 1]));