Given an array of integers, find the first missing positive integer in linear time and constant space. In other words, find the lowest positive integer that does not exist in the array. The array can contain duplicates and negative numbers as well. For example, the input [3, 4, -1, 1] should give 2. The input [1, 2, 0] should give 3.
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The Himalayas, or Himalaya is a mountain range in Asia, separating the plains of the Indian subcontinent from the Tibetan Plateau. The range has many of the Earth's highest peaks, including the highest, Mount Everest. The Himalayas include over fifty mountains exceeding 7,200 m (23,600 ft) in elevation, including ten of the fourteen 8,000-metre peaks. By contrast, the highest peak outside Asia (Aconcagua, in the Andes) is 6,961 m (22,838 ft) tall.
Lifted by the subduction of the Indian tectonic plate under the Eurasian Plate, the Himalayan mountain range runs west-northwest to east-southeast in an arc 2,400 km (1,500 mi) long. Its western anchor, Nanga Parbat, lies just south of the northernmost bend of Indus river. Its eastern anchor, Namcha Barwa, is just west of the great bend of the Yarlung Tsangpo River (upper stream of the Brahmaputra River). The Himalayan range is bordered on the northwest by the Karakoram and the Hindu Kush ranges. To the north, the chain is separated from the Tibetan Plateau by a 50–60 km (31–37 mi) wide tectonic valley called the Indus-Tsangpo Suture. Towards the south the arc of the Himalaya is ringed by the very low Indo-Gangetic Plain. The range varies in width from 350 km (220 mi) in the west (Pakistan) to 150 km (93 mi) in east (Arunachal Pradesh). The Himalayas are distinct from the other great ranges of central Asia, although sometimes the term 'Himalaya' (or 'Greater Himalaya') is loosely used to include the Karakoram and some of the other ranges.