增加二分法的变种应用

typescript/15_binarysearch/BinaryFind.ts

@@ -0,0 +1,115 @@
+/**
+ * 二分查找法在实际的场合使用不多
+ * 我们更多的是看到一些查找法的变种
+ */
+class BinaryFind {
+  /**
+   * 在数组中查找第一个等于给定值的位置
+   * @param array 给定的要查找的范围数组
+   * @param target 要查找的目标值
+   * @return 目标在数组中的位置
+   */
+  static findFirstElement(array: number[], target: number): number {
+    const length = array ? array.length : null
+    if (!length || length === 0) return -1
+    let low = 0
+    let high = length - 1
+    while (low <= high) {
+      const mid = low + ((high - low) >> 2)
+      if (array[mid] > target) {
+        high = mid - 1
+      } else if (array[mid] < target) {
+        low = mid + 1
+      } else {
+        if (mid === 0 || array[mid - 1] !== target) {
+          return mid
+        } else {
+          high = mid - 1
+        }
+      }
+    }
+    return -1
+  }
+
+  /**
+   * 在数组中查找最后一个等于给定值的位置
+   * @param array 给定的要查找的范围数组
+   * @param target 要查找的目标值
+   */
+  static findLastElement(array: number[], target: number): number {
+    const length = array ? array.length : null
+    if (!length || length === 0) return -1
+    let low = 0
+    let high = length - 1
+    while (low <= high) {
+      const mid = low + ((high - low) >> 2)
+      if (array[mid] > target) {
+        high = mid - 1
+      } else if (array[mid] < target) {
+        low = mid + 1
+        // 这里已经是找到相等的元素了
+      } else {
+        if (mid === length - 1 || array[mid + 1] !== target) {
+          return mid
+        } else {
+          low = mid + 1
+        }
+      }
+    }
+    return -1
+  }
+
+  /**
+   * 在数组中查找第一个大于等于给定值的位置
+   * @param array 给定的要查找的范围数组
+   * @param target 要查找的目标值
+   */
+  static findFirstElementGreaterThanTarget(array: number[], target: number): number {
+    const length = array ? array.length : null
+    if (!length || length === 0) return -1
+    let low = 0
+    let high = length - 1
+    while (low <= high) {
+      const mid = low + ((high - low) >> 2)
+      if (array[mid] < target) {
+        low = mid + 1
+      } else {
+        if (mid === 0 || array[mid - 1] < target) {
+          return mid
+        } else {
+          high = mid - 1
+        }
+      }
+    }
+    return -1
+  }
+
+  /**
+   * 在数组中查找最后一个小于等于给定值的位置
+   * @param array 给定的要查找的范围数组
+   * @param target 要查找的目标值
+   */
+  static findLastElementLessThanTarget(array: number[], target: number): number {
+    const length = array ? array.length : null
+    if (!length || length === 0) return -1
+    let low = 0
+    let high = length - 1
+    while (low <= high) {
+      const mid = low + ((high - low) >> 2)
+      if (array[mid] > target) {
+        high = mid - 1
+      } else {
+        if (mid === length - 1 || array[mid + 1] > target) {
+          return mid
+        } else {
+          low = mid + 1
+        }
+      }
+    }
+    return -1
+  }
+}
+
+const binaryFindTest = [1, 3, 4, 4, 5, 6, 8, 8, 8, 11, 18]
+const target = BinaryFind.findLastElementLessThanTarget(binaryFindTest, -1)
+console.log(target)