class modify

Author: 左程云

src/topinterviewquestions/Problem_0001_TwoSum.java

@@ -5,6 +5,7 @@
 public class Problem_0001_TwoSum {
 
 	public static int[] twoSum(int[] nums, int target) {
+		// key 某个之前的数   value 这个数出现的位置
 		HashMap<Integer, Integer> map = new HashMap<>();
 		for (int i = 0; i < nums.length; i++) {
 			if (map.containsKey(target - nums[i])) {

src/topinterviewquestions/Problem_0003_LongestSubstringWithoutRepeatingCharacters.java

@@ -1,24 +1,32 @@
 package topinterviewquestions;
 
+import java.util.HashMap;
+
 public class Problem_0003_LongestSubstringWithoutRepeatingCharacters {
 
-	public static int lengthOfLongestSubstring(String str) {
-		if (str == null || str.equals("")) {
+	public static int lengthOfLongestSubstring(String s) {
+		if (s == null || s.equals("")) {
 			return 0;
 		}
-		char[] chas = str.toCharArray();
+		char[] str = s.toCharArray();
+		// map (a, ?) (b, ?)
+		// a, 17
+		// map[97] = 17
 		int[] map = new int[256];
 		for (int i = 0; i < 256; i++) {
 			map[i] = -1;
 		}
+		// 收集答案
 		int len = 0;
-		int pre = -1;
+		int pre = -1; // i-1位置结尾的情况下，往左推，推不动的位置是谁
 		int cur = 0;
-		for (int i = 0; i != chas.length; i++) {
-			pre = Math.max(pre, map[chas[i]]);
+		for (int i = 0; i != str.length; i++) {
+			// i位置结尾的情况下，往左推，推不动的位置是谁
+			// pre (i-1信息) -> pre(i 结尾信息)
+			pre = Math.max(pre, map[str[i]]);
 			cur = i - pre;
 			len = Math.max(len, cur);
-			map[chas[i]] = i;
+			map[str[i]] = i;
 		}
 		return len;
 	}

src/topinterviewquestions/Problem_0004_MedianOfTwoSortedArrays.java

@@ -45,31 +45,47 @@ public static int findKthNum(int[] arr1, int[] arr2, int kth) {
 			}
 			return getUpMedian(shorts, kth - l, s - 1, longs, kth - s, l - 1);
 		}
+		// 第2段
 		if (longs[kth - s - 1] >= shorts[s - 1]) {
 			return longs[kth - s - 1];
 		}
 		return getUpMedian(shorts, 0, s - 1, longs, kth - s, kth - 1);
 	}
 
-	public static int getUpMedian(int[] a1, int s1, int e1, int[] a2, int s2, int e2) {
+	public static int getUpMedian(int[] A, int s1, int e1, int[] B, int s2, int e2) {
 		int mid1 = 0;
 		int mid2 = 0;
-		int offset = 0;
 		while (s1 < e1) {
 			mid1 = (s1 + e1) / 2;
 			mid2 = (s2 + e2) / 2;
-			offset = ((e1 - s1 + 1) & 1) ^ 1;
-			if (a1[mid1] > a2[mid2]) {
-				e1 = mid1;
-				s2 = mid2 + offset;
-			} else if (a1[mid1] < a2[mid2]) {
-				s1 = mid1 + offset;
-				e2 = mid2;
-			} else {
-				return a1[mid1];
+			if (A[mid1] == B[mid2]) {
+				return A[mid1];
+			}
+			if (((e1 - s1 + 1) & 1) == 1) { // 奇数长度
+				if (A[mid1] > B[mid2]) {
+					if (B[mid2] >= A[mid1 - 1]) {
+						return B[mid2];
+					}
+					e1 = mid1 - 1;
+					s2 = mid2 + 1;
+				} else { // A[mid1] < B[mid2]
+					if (A[mid1] >= B[mid2 - 1]) {
+						return A[mid1];
+					}
+					e2 = mid2 - 1;
+					s1 = mid1 + 1;
+				}
+			} else { // 偶数长度
+				if (A[mid1] > B[mid2]) {
+					e1 = mid1;
+					s2 = mid2 + 1;
+				} else {
+					e2 = mid2;
+					s1 = mid1 + 1;
+				}
 			}
 		}
-		return Math.min(a1[s1], a2[s2]);
+		return Math.min(A[s1], B[s2]);
 	}
 
 }