huhu的小世界

1
//arr数组必须有序
2
public static boolean exist (int[] arr ,int target) {
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    if (arr == null || arr.length == 0) {
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        return false;
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    }
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    int l = 0 ,r = arr.length - 1;
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    while (l <= r) {
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        int mid = l + ((r - l) >> 1);
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        if (arr[mid] < target) {
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            l = mid + 1;
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        } else if (arr[mid] > target) {
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            r = mid - 1;
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        } else {
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            return true;
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        }
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    }
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    return false;
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}

1
//arr数组必须有序
2
public static int findTargetLeft (int[] arr ,int target) {
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    int ans = -1;
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    if (arr == null || arr.length == 0) {
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        return ans;
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    }
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    int l = 0 ,r = arr.length - 1;
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    while (l <= r) {
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        int mid = l + ((r - l) >> 1);
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        if (arr[mid] >= target) {
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            ans = mid;
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            r = mid - 1;
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        } else {
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            l = mid + 1;
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        }
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    }
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    return ans;
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}

1
//arr数组必须有序
2
public static int findTargetRight (int[] arr ,int target) {
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    int ans = -1;
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    if (arr == null || arr.length == 0) {
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        return ans;
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    }
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    int l = 0 ,r = arr.length - 1;
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    while (l <= r) {
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        int mid = l + ((r - l) >> 1);
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        if (arr[mid] <= target) {
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            ans = mid;
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            l = mid + 1;
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        } else {
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            r = mid - 1;
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        }
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    }
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    return ans;
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}

1
//数组相邻元素不相等、峰值定义为严格大于两侧邻居
2
public static int findPeak (int[] arr) {
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    int n = arr.length;
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    if (n == 0) {
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        return -1;
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    }
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    if (arr.length == 1) {
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        return 0;
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    }
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    if (arr[0] > arr[1]) {
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        return 0;
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    }
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    if (arr[n - 1] > arr[n - 2]) {
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        return n - 1;
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    }
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    int l = 1 ,r = n - 2 ,ans = -1;
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    while (l <= r) {
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        int mid = l + ((r - l) >> 1);
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        if (arr[mid - 1] > arr[mid]) {
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            r = mid - 1;
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        } else if (arr[mid] < arr[mid + 1]) {
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            l = mid + 1;
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        } else {
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            ans = mid;
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            break;
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        }
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    }
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    return ans;
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}