Merge pull request #9 from Subham1999/back_tracking

Back tracking

Author: Subham1999

.idea/workspace.xml

@@ -0,0 +1,10 @@
+package com.thealgorithm.array;
+
+/**
+ * @author: Subham Santra
+ */
+public class TheThreeSum {
+  public static void main(String[] args){
+
+  }
+}

data-structures/src/main/java/com/thealgorithm/array/TheThreeSum.java

@@ -0,0 +1,83 @@
+package com.thealgorithm.binsearch;
+
+/**
+ * @author: Subham Santra
+ */
+public class CapacityToShipPackagesWithInDDays {
+
+  public int shipWithinDays(int[] weights, int days) {
+    int n = weights.length;
+    int[] prefixSum = new int[n + 1];
+    int weightMin = Integer.MIN_VALUE;
+
+    for (int i = 0; i < n; ++i) {
+      prefixSum[i + 1] = prefixSum[i] + weights[i];
+      weightMin = Math.max(weightMin, weights[i]);
+    }
+
+    int weightMax = prefixSum[prefixSum.length - 1];
+
+    int ans = Integer.MAX_VALUE;
+
+    while (weightMin <= weightMax) {
+      int mid = (weightMax + weightMin) / 2;
+      int checkDays = checkDays(prefixSum, mid, 1, n);
+      System.out.printf("midWeight = %d days = %d\n", mid, checkDays);
+      if (checkDays <= days) {
+        ans = mid;
+        weightMax = mid - 1;
+      } else {
+        weightMin = mid + 1;
+      }
+    }
+
+    return ans;
+  }
+
+  private int checkDays(int[] prefixSum, int weight, int lo, int hi) {
+    if (lo > hi) {
+      return 0;
+    }
+    if (lo == hi) {
+      return (prefixSum[lo] - prefixSum[lo - 1]) <= weight ? 1 : 0;
+    }
+    int pos = lowerBound(prefixSum, lo, weight);
+    if (pos == -1) {
+      return Integer.MAX_VALUE;
+    }
+    return 1 + checkDays(prefixSum, weight, pos + 1, hi);
+  }
+
+  private int lowerBound(int[] prefixSum, int lo, int target) {
+    int right = prefixSum.length - 1;
+    int left = lo;
+    int pos = -1;
+    while (left <= right) {
+      int mid = (left + right) / 2;
+      int midWeight = querySum(prefixSum, lo, mid);
+      if (midWeight <= target) {
+        pos = mid;
+        left = mid + 1;
+      } else {
+        right = mid - 1;
+      }
+    }
+    return pos;
+  }
+
+  private int querySum(int[] prefixSum, int lo, int hi) {
+    return prefixSum[hi] - prefixSum[lo - 1];
+  }
+
+  public static void main(String[] args) {
+    System.out.println(
+        new CapacityToShipPackagesWithInDDays().shipWithinDays(new int[] {3, 2, 2, 4, 1, 4}, 3));
+
+    System.out.println(
+        new CapacityToShipPackagesWithInDDays().shipWithinDays(new int[] {1, 2, 3, 1, 1}, 4));
+
+    System.out.println(
+        new CapacityToShipPackagesWithInDDays()
+            .shipWithinDays(new int[] {1, 2, 3, 4, 5, 6, 7, 8, 9, 10}, 5));
+  }
+}

data-structures/src/main/java/com/thealgorithm/binsearch/CapacityToShipPackagesWithInDDays.java

@@ -0,0 +1,47 @@
+package com.thealgorithm.binsearch;
+
+/**
+ * @author: Subham Santra
+ */
+public class KokoEatingBananas {
+  public int minEatingSpeed(int[] piles, int h) {
+    long hi = 0L;
+    long lo = 1;
+    for (int pile : piles) {
+      hi = Math.max(pile, hi);
+    }
+    // System.out.printf("Range speed %d to %d\n", lo, hi);
+    // start binary search
+    long minimumSpeed = 1L;
+    while (lo <= hi) {
+      long mid = ((hi - lo) >> 1) + lo;
+      long kokoFinishTime = kokoFinishTime(piles, mid);
+      // System.out.printf("finish time %d for speed %d\n", kokoFinishTime, mid);
+      if (kokoFinishTime <= h) {
+        // Taking exact same time or even less, we shall reduce speed and check
+        minimumSpeed = mid;
+        hi = mid - 1;
+      } else {
+        // Taking more time to finish, to reduce time, we need to increase speed
+        lo = mid + 1;
+      }
+    }
+    return (int) minimumSpeed;
+  }
+
+  long kokoFinishTime(int[] piles, long speed) {
+    long carry = 0L;
+    for (double pile : piles) {
+      carry += (long) Math.ceil(pile / speed);
+    }
+    return carry;
+  }
+
+  public static void main(String[] args) {
+    System.out.println(new KokoEatingBananas().minEatingSpeed(new int[] {3, 6, 7, 11}, 8));
+    System.out.println(new KokoEatingBananas().minEatingSpeed(new int[] {100}, 99));
+    System.out.println(
+        new KokoEatingBananas()
+            .minEatingSpeed(new int[] {805306368, 805306368, 805306368}, 1000000000));
+  }
+}

data-structures/src/main/java/com/thealgorithm/binsearch/KokoEatingBananas.java

@@ -0,0 +1,61 @@
+package com.thealgorithm.miscelleneous;
+
+import com.thealgorithm.commons.Pair;
+import java.util.HashSet;
+import java.util.Set;
+
+/**
+ * @author: Subham Santra
+ */
+public class WalkingRobotSimulation {
+
+  static class Solution {
+    public int robotSim(int[] commands, int[][] obstacles) {
+
+      Set<Pair<Integer, Integer>> obstacleSet = new HashSet<>();
+      for (int[] obs : obstacles) {
+        obstacleSet.add(Pair.of(obs[0], obs[1]));
+      }
+
+      int[] current = new int[2];
+
+      char direction = 'e';
+
+      int max = 0;
+
+      for (int command : commands) {
+        if (command < 0) {
+          direction = changeDirection(direction, command == -1);
+        } else {
+          // move(dir, current, command, obstacleSet);
+          int x = current[0];
+          int y = current[1];
+
+          for (int c = 1; c <= command; ++c) {
+            int xx = x + (direction == 'e' ? 1 : (direction == 'w' ? -1 : 0));
+            int yy = y + (direction == 'n' ? 1 : (direction == 's' ? -1 : 0));
+            if (obstacleSet.contains(Pair.of(xx, yy))) {
+              break;
+            }
+            current[0] = x = xx;
+            current[1] = y = yy;
+            max = Math.max(max, (int) Math.sqrt(x * x + y * y));
+          }
+        }
+      }
+      return max;
+    }
+
+    char changeDirection(char dir, boolean left) {
+      return switch (dir) {
+        case 'e' -> left ? 'n' : 's';
+        case 'n' -> left ? 'w' : 'e';
+        case 'w' -> left ? 's' : 'n';
+        case 's' -> left ? 'e' : 'w';
+        default -> '0';
+      };
+    }
+  }
+
+  public static void main(String[] args) {}
+}