modify on class

Author: 左程云

src/topinterviewquestions/Problem_0045_JumpGameII.java

@@ -6,17 +6,20 @@ public static int jump(int[] arr) {
 		if (arr == null || arr.length == 0) {
 			return 0;
 		}
-		int jump = 0;
+		int step = 0;
 		int cur = 0;
-		int next = 0;
-		for (int i = 0; i < arr.length; i++) {
+		int next = arr[0];
+		for (int i = 1; i < arr.length; i++) {
+//            if(next >= arr.length - 1){
+//                return step + 1;
+//            }
 			if (cur < i) {
-				jump++;
+				step++;
 				cur = next;
 			}
 			next = Math.max(next, i + arr[i]);
 		}
-		return jump;
+		return step;
 	}
 
 }

src/topinterviewquestions/Problem_0045_JumpGameIIFollowUpOnClass.java

@@ -6,6 +6,80 @@
 
 public class Problem_0045_JumpGameIIFollowUpOnClass {
 
+	// start 和 end从1开始
+	public static int jump1(int N, int start, int end, int[] arr) {
+		boolean[] walk = new boolean[N];
+		return f(arr, N, end, start, walk);
+	}
+
+	// 从i位置到end，至少要几步
+	// walk[i-1] == false i之前没到过
+	// walk[i-1] == true i之前到过
+	public static int f(int[] arr, int N, int end, int i, boolean[] walk) {
+		if (i < 1) {
+			return -1;
+		}
+		if (i > N) {
+			return -1;
+		}
+		if (walk[i - 1]) {
+			return -1;
+		}
+		if (i == end) {
+			return 0;
+		}
+		walk[i - 1] = true;
+		int left = i - arr[i - 1];
+		int right = i + arr[i - 1];
+		int next = -1;
+		int ans1 = f(arr, N, end, left, walk);
+		int ans2 = f(arr, N, end, right, walk);
+		if (ans1 != -1 && ans2 != -1) {
+			next = Math.min(ans1, ans2);
+		} else if (ans1 != -1) {
+			next = ans1;
+		} else if (ans2 != -1) {
+			next = ans2;
+		}
+		walk[i - 1] = false;
+		if (next == -1) {
+			return -1;
+		}
+		return next + 1;
+	}
+
+	public static int jump2(int N, int start, int end, int[] arr) {
+		return g(arr, N, end, start, 0);
+	}
+
+	public static int g(int[] arr, int N, int end, int i, int k) {
+		if (i < 1) {
+			return -1;
+		}
+		if (i > N) {
+			return -1;
+		}
+		if (k > N - 1) {
+			return -1;
+		}
+		if (i == end) {
+			return k;
+		}
+		int left = i - arr[i - 1];
+		int right = i + arr[i - 1];
+		int ans = -1;
+		int ans1 = g(arr, N, end, left, k + 1);
+		int ans2 = g(arr, N, end, right, k + 1);
+		if (ans1 != -1 && ans2 != -1) {
+			ans = Math.min(ans1, ans2);
+		} else if (ans1 != -1) {
+			ans = ans1;
+		} else if (ans2 != -1) {
+			ans = ans2;
+		}
+		return ans;
+	}
+
 	public static int jumpMinTimes1(int N, int start, int end, int[] arr) {
 		boolean[] map = new boolean[N + 1];
 
@@ -174,15 +248,15 @@ public static void printArray(int[] arr) {
 	public static void main(String[] args) {
 		int maxN = 20;
 		int maxV = 10;
-		int testTimes = 200000;
+		int testTimes = 200;
 		System.out.println("test begin");
 		for (int i = 0; i < testTimes; i++) {
 			int[] arr = gerRandomArray(maxN, maxV);
 			int N = arr.length;
 			int start = (int) (Math.random() * N) + 1;
 			int end = (int) (Math.random() * N) + 1;
-			int ans1 = jumpMinTimes1(N, start, end, arr);
-			int ans2 = jumpMinTimes2(N, start, end, arr);
+			int ans1 = jump1(N, start, end, arr);
+			int ans2 = jump2(N, start, end, arr);
 			int ans3 = jumpMinTimes3(N, start, end, arr);
 			if (ans1 != ans2 || ans2 != ans3) {
 				printArray(arr);

src/topinterviewquestions/Problem_0046_Permutations.java

@@ -1,10 +1,42 @@
 package topinterviewquestions;
 
 import java.util.ArrayList;
+import java.util.HashSet;
 import java.util.List;
 
 public class Problem_0046_Permutations {
 
+	public static List<List<Integer>> onClass(int[] nums) {
+		List<List<Integer>> ans = new ArrayList<>();
+		HashSet<Integer> rest = new HashSet<>();
+		for (int num : nums) {
+			rest.add(num);
+		}
+		ArrayList<Integer> path = new ArrayList<>();
+		f(rest, path, ans);
+		return ans;
+	}
+
+	// rest中有剩余数字，已经选过的数字不在rest中，选过的数字在path里
+	public static void f(HashSet<Integer> rest, ArrayList<Integer> path, List<List<Integer>> ans) {
+		if (rest.isEmpty()) {
+			ans.add(path);
+		} else {
+			for (int num : rest) {
+				ArrayList<Integer> curPath = new ArrayList<>(path);
+				curPath.add(num);
+				HashSet<Integer> clone = cloneExceptNum(rest, num);
+				f(clone, curPath, ans);
+			}
+		}
+	}
+
+	public static HashSet<Integer> cloneExceptNum(HashSet<Integer> rest, int num) {
+		HashSet<Integer> clone = new HashSet<>(rest);
+		clone.remove(num);
+		return clone;
+	}
+
 	public static List<List<Integer>> permute(int[] nums) {
 		List<List<Integer>> ans = new ArrayList<>();
 		process(nums, 0, ans);

src/topinterviewquestions/Problem_0055_JumpGame.java

@@ -8,6 +8,9 @@ public static boolean canJump(int[] nums) {
 		}
 		int max = nums[0];
 		for (int i = 1; i < nums.length; i++) {
+//			if (max >= nums.length - 1) {
+//				return true;
+//			}
 			if (i > max) {
 				return false;
 			}